The Lions are through the draft and at least the bulk of free agency. The talent base of their 2019 roster is essentially set, and the challenge for Matt Patricia and his coaching staff now will be to figure out the best combinations of starters to form a complete team.

Detroit made some significant investments in free agency and added nine players in the draft, working a significant overhaul from last year's 6-10 team. Here are the three strongest and the three weakest positions heading into the on-field portions of the offseason:

Mike Mulholland | MLive.com

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1. Defensive tackles

No position group has transformed for the better in Detroit over the past calendar year than the defensive line has. Specifically, Patricia said he was going to build his defense from the middle out, and that is what has followed. The midseason trade for Damon "Snacks" Harrison was a game-changer for the Lions run defense, taking it from one of the most gashed units in the league to one that finished 13th in Football Outsiders' DVOA metric for performance against the league average. In addition to leading all interior defensive linemen with 46 run stops, "Snacks" also posted 3.5 sacks in 10 games with the Lions.

Adding that 6-foot-3-inch, 355-pound traditional nose tackle allowed A'Shawn Robinson to make the gains the team had been waiting for since his rookie season. and brighter days should lie ahead as he enters a contract year at age 24. Where this duo might lack in pass rushing, it makes up with third-down contributions from Da'Shawn Hand and ends such as Trey Flowers and Romeo Okwara, who can line up in their spots on obvious passing downs.

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Mike Mulholland | MLive.com

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2. Running backs

Another position group that has gone from one of the biggest weaknesses to one of the top strengths is running back. That transformation started with a trade up in the second round last year to draft Kerryon Johnson following a career as Auburn's bell cow. He wasn't quite that in Detroit, as he ran into some more durability problems as the year progressed, but he was terrific when he was on the field. His 5.4 yards per carry ranked second in the NFL. He broke the long 100-yard rushing drought twice. And he added 32 receptions on 39 targets in the passing game.

Detroit's rushing attack fell off after Johnson's knee injury last season, but it should be better this year. Replacing the ancient and impatient LeGarrette Blount is C.J. Anderson, who might not look the part but has done nothing but get the job done every single place he has played. At 5 feet 8 inches and 225 pounds, Anderson is a 4.5-yards-per-carry rusher throughout his career and was a revelation with the Rams late last year, helping to power them to the Super Bowl. He'll fill the short-yardage and No. 2 role better than Blount did, Zach Zenner showed late last year that he can provide some quality running as well. Theo Riddick has appeared to lose a step as a receiver but is still a very strong pass protector.

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Mike Mulholland | MLive.com

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3. Quarterbacks

Yes, Matthew Stafford is coming off the worst season of his career, and if this list just ranked 2018 performance, he'd be closer to one of the weak links than a strength. But this is about projecting the most likely scenarios for 2019, and it's hard to not envision a bounceback for a 10-year pro given where the skill positions around him should return to and how those play into the ability of a quarterback to play to his highest level.

From 2015-2018, Stafford performed like a top-10 quarterback with consistency, averaging 28 touchdowns to 11 interceptions with 7.6 adjusted yards per attempt and a quarterback rating of at least 93.3 in all three seasons. Last year saw an obvious drop, namely in his explosive plays, but he still finished with 10 more touchdowns than interceptions and a quarterback rating of 89.9.

Whereas other positions fall off with age, quarterbacks are just as likely to get better as they enter their 30s and rack up more experience and understanding. Depth also matters little when one player plays and that particular player hasn't missed a game since 2010. It remains to be seen how Stafford meshes with Darrell Bevell's new offense, but it's not hard to envision him at least returning to the norm with a healthy Marvin Jones, Kenny Golladay and T.J. Hockenson to catch the ball.

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1. Guards

I want to preface this section by saying that this team does not have the clear top weakness this year that it has had in past years. It was easy before to just pencil in tight end or defensive line immediately. Those positions at times ranked among the weakest on any team in the league. This year feels different, but the Lions still have some positions that raise major questions heading into practices.

One of those is guard. Detroit has Frank Ragnow back after an improving if not flashy rookie season, and his extra year of understanding, strength and especially confidence in the system should result in plus performance, not to mention the chemistry he built between Taylor Decker and Graham Glasgow.

This ranking is all about the right guard position, which is the one area the Lions left mostly unaddressed this offseason. They released T.J. Lang, signed a veteran journeyman with Bevell ties in Oday Aboushi and then did not select one in the draft before signing a projected Day 3 pick in Beau Benzschawel in the undrafted stages. The rookie has some potential, but he has so much to develop in his pass protection that it'd be hard to see him starting this season. It'll likely come down to Aboushi and Kenny Wiggins, who filled in for Lang last year and has a similar journeyman profile to Aboushi. Perhaps one of them surprises, but right now, this is the one clear spot where it appears the Lions will be taking a backup and making him a starter, and it's a position they value highly with the balanced approach they're looking to take.

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Mike Mulholland | MLive.com

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2. Linebackers

The Lions didn't see too much reason to shake up their linebacking corps after a suspect 2018 season, as they kept the position coach and three starters without signing any competition. The change came in the second round of the draft, when they surprised some by taking Hawaii's Jahlani Tavai despite the fact that he is coming off shoulder surgery.

This position group has the potential to fluctuate greatly based on how the Tavai pick turns out and how that enables Jarrad Davis and Devon Kennard to develop and play more to their strengths, but there's just a lot of unknown in that dynamic. Davis has yet to put together a full season that looks anything close to first-round value. He and Kennard brought some pass rushing to the unit last year and helped handle options and stretch runs, but the center of the run defense remained leaky, and so did coverage of backs and tight ends at times.

This ranking might change based on what Tavai can show between now and the season, as he was drafted to handle some read-and-react duties to allow Davis to rush even more. That could work well. It could also be such a work in progress that this group lags behind for another year.

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Mike Mulholland | MLive.com

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3. Safeties

This group might surprise a few people, but it's based as much on that idea of the unknown as anything else. The Lions were pretty bad here last year, with Glover Quin miscast and speed lacking to cover much of anyone. And so while Quin's departure isn't exactly a huge loss in talent, it does create a hole without a proven commodity, and it's hard to fully account for what his loss in leadership might amount to.

Quandre Diggs is a solid player who fits a versatile scheme, and he will take on some leadership responsibilities, but he's a much different type in that way than Quin. Around him are plenty of questions. Tracy Walker flashed a little last year but with no starts and just two pass deflections, it's hard to know how a player who last started at Louisiana-Lafayette will handle open-field responsibilities in a passing league. Plenty of the same can be said for third-round Boston College product Will Harris, who has much athleticism but could see a learning curve in coverage and in tackling. Tavon Wilson is 29, and though he'll help teach the scheme, it's somewhat telling that he took a pay cut to remain on the roster.

Patricia likes to play four safeties at least 20 percent of the time, and so while Detroit isn't exactly thin here, it does have multiple players who project as major question marks in major roles. This should be a position that gets better as young players get up to speed, but in April, it's still one of the weaker units altogether.

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Mike Mulholland | MLive.com

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"But what about..."

I put this question out on Twitter initially, as I knew answers for strengths and weaknesses would be all over the map. It's a much harder roster to judge right now than in past years, when Calvin Johnson and Glover Quin made some positions strengths and totally unproven commodities made others weaknesses. So to address a few suggestions:

Tight end: Last year, this was the weakest position by far. It's been overhauled with Jesse James and No. 8 overall pick T.J. Hockenson, but that doesn't yet make it a strength in my eyes. James was a No. 2 in Pittsburgh and should be that here. History shows rookie tight ends need a while before they're all that productive. Detroit wants two good starters at this spot so it can run or pass at will. A weakness doesn't become a strength until it proves it is.

Edge rusher: Ironically, I think you could have made an argument for this as a fringe strength or fringe weakness depending on how you view it. Detroit's speed rushing should still lag behind, though it's trying to make up for that with Davis and some third-down interior play. Trey Flowers certainly helps the edge play, and Hand should play more there this year as well. It's more of a strength than not but not clearly on one side or another yet.

Wide receiver: Marvin Jones and Kenny Golladay are very good. The guys behind them are not. So how do you rank that? I judged these position groups as a whole, and the top four pieces or so all matter for a position like this. It's neither a strength nor a weakness, but an injury could push it to the latter.

Cornerback: Darius Slay and Justin Coleman give this group a real chance to be a strength this year, as we've already seen what Coleman can do in a Patriots-style defense. The third outside spot is just such a question mark still, with a fifth-round rookie in Amani Oruwariye competing with an up-and-down veteran in Rashaan Melvin to start. That could work, but any weakness becomes a major problem at that position in this kind of league. We need to see a little more first.