The Denver Broncos believe the best is yet to come for Case Keenum, a 30-year-old just scratching the surface of his starting potential.

Around the NFL, however, his standing isn't so high.

In releasing his 2018 quarterback rankings, which are separated into four tiers, ESPN's Mike Sando talked with an anonymous offensive coach who not-so-subtly knocked Keenum's Tier 3 classification, tied for 23rd overall.

"He's a 3 on his best day," the coach said. "They had defense and really good receiving talent for him in Minnesota, and they had enough rushing attempts where it was not all on him and they mixed the play-action so he could survive. What is the difference between Case Keenum and Nick Foles?"

Sando answered that Keenum is better equipped to face a pass rush.

"Yeah, maybe," the coach replied, "but they are high-end backups who got opportunities with teams that had both sides of the ball ready to go. I just do not think Keenum all of a sudden got good."

Get access to Denver Broncos inside info, deep-dive analysis and in-depth film reviews! Don't wait – become a Mile High Huddle VIP subscriber today!

An unnamed defensive coordinator, though less harshly, agreed with the assessment that Keenum is backup material.

"He is one of those guys who will have a couple good years and then he will go to be a good backup and at the end of the day he is going to play 12-13 years in the league and he'll be fine -- like Josh McCown," the coordinator said.

Sando, who said the new Broncos starter is "a 4 who played like a 2" in 2017, explains Tier 3 guys are "legitimate" QBs that need "a heavier running game and/or defense to win. A lower-volume passing offense makes his job easier."

This perfectly sums up Denver's current configuration -- a run-first attack, led by a committee backfield, on offense and a still-elite defense buoying the team. They're well aware of Keenum's strengths and weaknesses, and paid him accordingly with a two-year, $36 million deal.

"Keenum has confidence and he's calm in the pocket," a former general manager told Sando. "He doesn't get frantic and make stupid decisions. He has just enough arm strength to make the throws. He won, and he went from nothing to something."

What cannot be overstated enough is Keenum on his worst day represents an upgrade over the likes of Trevor Siemian, Paxton Lynch and Brock Osweiler, the troika they trotted out last season. And interestingly, he was lumped in the same tier as Kirk Cousins, Alex Smith, Eli Manning, Dak Prescott and Joe Flacco, among others.

Put a Manning or Smith on the Broncos and they make the playoffs. Why is it any different with Keenum?

Answer: It's not.