I have a somewhat different take on this.
The staff deserves credit for identifying him as someone who, as a freshman, would outperform their recruiting ranking. I'd say many of us were pleasantly surprised by what a sub-200 recruit could give us right off the bat.
The staff did not, by any means, develop him. He was, at best, incrementally better in years 2-4 than he was in year 1.
If the staff wants to take credit for anything, it's identifying underrated talent, not developing that talent.
I think some of the subtle leaps that he made get distorted for a couple reasons:
1. While the coaching staff may have done a good job with him developmentally, they did not do a good job with him on game day. Too often they designed breakneck, hard-hedging schemes that worked with guys like Phil Nolan and Giffey and Daniels but not Brimah, who needed to be more paint bound.
2. For all the things he got better at, he never really shook his one fatal flaw of picking up fouls. He went from 4.3 fouls per 40 minutes as a sophomore to 4.9 as a junior to 5.2 as a senior. You can't have that from a player you're counting on to be a cog in the machine and that he did not improve in that area is his responsibility.
3. Dude was just a frustrating player and, much like Purvis, his flaws would jump off the screen in such a way that it caused us to understate his value. When you can't do things that a fan can do - like consistently catch the ball, track the ball off the rim, and keep your pivot foot - you begin to lose the benefit of the doubt.
But the one thing fans crushed him for throughout his career was rebounding, and by his senior year, he had gone from a 10.2% rebounding rate as a sophomore to 12.6% as a junior to 13.9% as a senior. His defensive rebounding rate went from 10.8% to 14.1% to 17.7% this season. That isn't a small jump, and during conference play he averaged 8 points, 7 rebounds, and 3 blocks per game. That's more than enough from a UConn center most years (especially given all of his advanced numbers - like box +/-, offensive/defensive rating, PER - ranked among the best on the team all three years he started), but this season, he was flanked by a crew that represented an enormous devolution from where he started as a freshman, surrounded by talented, smart players.
A lot of this is circumstantial, and when we claim he hasn't improved, it does not account for all of the variables that influenced our perception. Some of the s hit we saw this year - throwing bounce passes at his feet, force-feeding him in the post, using him as a primary screener - doesn't happen on better, more complete teams.
Facey, for instance, is billed as a feather in the staff's cap, but I would actually argue he improved less than Brimah. It's just that, he always had better players in front of him.