When former Bears coach John Fox said on ESPN’s “NFL Live” last month that the Bears had the worst offseason in the NFL, it came off as sour grapes. Still, Fox wasn’t off-base in his rationalization — the Bears’ defense will be challenged to match last season’s takeaway total (36). And the kicker is a problem until the Bears prove it’s not.

And truth be told, the Bears didn’t have an eye-opening offseason on paper. Two of their key free-agency signings — safety Ha Ha Clinton-Dix and nickelback Buster Skrine — are not certain upgrades over Adrian Amos and Bryce Callahan. And the only thing we really know about Cordarrelle Patterson at this point is that he will not return a kickoff for a touchdown against the Bears this season.

In the draft, the Bears’ top addition, running back David Montgomery, was a third-round pick who is a piece of the puzzle more than a cornerstone of the foundation. Any of the other drafted and undrafted players — including wide receiver Riley Ridley (fourth round) and cornerback Duke Shelley (fifth round) could become big hits, but might not be a factor at all in 2019.

Then again, this truth can’t be ignored: The Bears’ offseason was so modest because their previous offseason was so fruitful. Linebackers Khalil Mack and Roquan Smith, tight end Trey Burton, receivers Allen Robinson, Taylor Gabriel and Anthony Miller, guard James Daniels and defensive lineman Bilal Nichols are a big reason why the Bears didn’t have many holes to fill — with 20 of 22 returning starters in 2019.

While newcomers Mack, Smith, Burton et al. last season fueled the jump from 5-11 to 12-4 in 2018, the Bears are counting on growth from within to take the next step in 2019. It’s easy to point to the loss of defensive coordinator Vic Fangio as a hole that will be difficult to fill. But, theoretically, Roquan Smith of 2019 should be significantly better than Roquan Smith of 2018 — an upgrade that tends to get overlooked when analyzing offseason additions.

You can’t assume anything in the NFL. But coming off a playoff season, the Bears are a quality young team with room to grow. Among returning returning starters and likely rotation players, their average age is 26.1 — 25.7 on offense; 26.6 on defense. Only four players will be 30 on opening day: guard Kyle Long (30), tackle Bobby Massie (30), cornerback Prince Amukamara (30) and Skrine (30).

Included in that group are nine returning players, all 25 and under, with potential if not expectations of self-upgrading the Bears at key positions:

Mitch Trubisky, 25, quarterback: After making the Pro Bowl as an alternate in his first full year as a starter — ranking 16th in the NFL in passer rating (95.4) and third in total QBR (70.3) — Trubisky is being counted on to take an even bigger step in 2019.

Roquan Smith, 22, linebacker: With a year of NFL experience and no contract holdout to keep him from training camp/preseason, Smith figures to bloom as a rising star in Chuck Pagano’s defense.

Anthony Miller, 24, wide receiver: Flashed enough while playing through a shoulder injury as a rookie to warrant expectations of a significant jump in production in his second NFL season.

James Daniels, 21, center: After an impressive rookie season at left guard, Daniels — who turns 22 on Sept. 13 — is expected to flourish at center, where he excelled in high school and at Iowa.

Eddie Goldman, 25, nose tackle: Already an accomplished player and four-year starter, Goldman still is growing as a player and on pace to achieve Pro Bowl recognition in 2019.

Tarik Cohen, 24, running back: A Pro Bowl kick returner in 2018, Cohen’s versatility and big-play ability makes him a particularly intriguing threat as a gadget player in Nagy’s offense.

Eddie Jackson, 25, safety: With five touchdowns in two seasons and All-Pro recognition last year, Jackson has set the bar high, but he is far from a finished product as an all-around safety.

Bilal Nichols, 22, defensive lineman: The fifth-round pick from Delaware made ESPN.com’s all-rookie team with three sacks, two forced fumbles, a fumble recovery and five TFLs last year. In a great spot to make a bigger impact in 2019.

Adam Shaheen, 24, tight end: The 2017 second-round pick has yet to live up to high expectations — he played only six games because of an injury last year. The Nagy offense figures to be a litmus test, similar to Kevin White last year.