Fair or not, having expectations that are driven by 1) what you've proven you can do and 2) how well you recruit is a reasonable.
Barnes' recruiting has not dropped off; if anything it has slightly improved the last 8 years compared to his first 10 at Texas. Barnes had a 7 year run with 2 league titles, 5 Sweet 16s, 3 Elite 8s, and 1 Final Four. He still recruits at a very high level and we know that he is capable of winning this league and making deep tournament runs, yet he's gone 8 years with nothing even close to that previous 7 years span. Yeah, he's still a successful coach compared to a lot of places, but compared to the bar he set for himself and the amount of talent he recruits (basically 3 Top 100s and 1 MCD AA per year) I find it hard to say he's being successful based on the expectations he's set for his program.