Seniors from big-time programs were among those who visited team headquarters this offseason.

DENVER — For whatever reason, defensive linemen take a while.

Malik Jackson, a fifth-round pick in 2012, did nothing for the Broncos as a rookie. He was a dominant force in their Super Bowl 50 season of 2015, his fourth, and wound up getting paid $45 million over three years with Jacksonville.

Adam Gotsis, a second-round pick in 2016, did nothing for the Broncos as a rookie. He didn’t start coming into his own until last year, his third, when several Broncos’ coaches thought he was the team’s best defensive lineman.

Shelby Harris, a seventh-round pick of Oakland in 2014, did little until his fourth season in 2017, first with the Broncos.

DeMarcus Walker, a second-round pick in 2017, is still taking a while.

This is why I think the 2019 NFL Draft class has a chance to be one of the weakest in 10 years – since the Tyson Jackson, Aaron Curry, Mark Sanchez, Knowshon Moreno, Robert Ayers draft of 2009.

This year’s class appears strong in defensive linemen, both in quality at the top and depth in the middle rounds.

It does not appear to have a bumper crop of prospects at the premium positions of quarterback, offensive tackles, cornerbacks and edge rushers. There also doesn’t appear to be a Julio Jones or A.J. Green-type at receiver, or Ezekiel Elliott, Todd Gurley or Christian McCaffrey at running back.

Drafter beware.

Still, it's incumbent upon Broncos' general manager John Elway and his top assistant to find their sleepers like Clay Matthews, Jared Cooks and T.J. Lang.

Based on their offseason vetting of draft picks, it seems certain the Broncos will select a defensive lineman. Maybe not with their No. 10 pick, although there have been some mocksters who have the Broncos taking Houston defensive lineman Ed Oliver.

More likely the Broncos would get their defensive lineman somewhere in rounds 2 through 4, at least based on their pre-draft visit pattern.

Broncos’ nose tackle Domata Peko was not retained and defensive end Derek Wolfe is in the final year of his contract.

“We’re just commodities in the business,’’ Wolfe said two weeks ago when asked about the draft process.

From the 13 Broncos’ pre-draft visits reported by 9News, four have been defensive linemen who are projected by NFL Draft Bible to go in the second through the fourth rounds: Jerry Tillery, Charles Omunihu, Dre’Mont Jones and Kingsley Keke.

All took a while to become productive at their respective programs. A closer look at those four defensive linemen:

Jerry Tillery, 6-6, 295, Notre Dame, 2nd round

Some draft sites think he can go in the first round. A physical specimen who had 1.0 sack and 5.5 tackles for loss combined in his first two years for the Fighting Irish, but a combined 11.5 sacks and 17.5 tackles for loss combined in his upperclassmen seasons.

Charles Omenihu, 6-5, 280, Texas, 2nd round

Has impressive 36-inch-plus arm length. Had no sacks as a freshman, then 3.0 as a sophomore and 4.0 as a junior before exploding for 9.5 sacks as a senior, along with 18.0 tackles for loss.

Omenihu explains why player evaluation is such an inexact science. Many of the top prospects leave college after their redshirt sophomore or junior seasons. Do you take them while projecting they have not yet reached their potential and have a high ceiling? Or do you take the more finished product who played his senior year but perhaps doesn’t have as much room to grow?

Elway and Russell went exclusively with four-year senior prospects with their first six picks through the first four rounds last year. A year later, the 2018 draft has been widely acclaimed as their best since at least 2012, when they nabbed the likes of Wolfe, Jackson and Danny Trevathan.

But the true evaluation of Broncos’ 2018 draft class will come in 2021.

Dre’Mont Jones, 6-2 ½, 281, Ohio State, 3rd round

Regarded somewhat as a disappointment until he had a monster senior season with 8.5 sacks and 13.0 tackles for loss. He had just 1.0 sack and 9.0 tackles for loss in his first three seasons combined.

Kingsley Keke, 6-2 ½, 288, Texas A&M, 4th round