Sure he went 12-0 at Houston in the regular but lost the championship game. Briles went 10-4 in winning his title. Other than one recruiting class there, his classes ranked very similar to Briles. I'll give you that the teams preceding Briles were poorly coached, but the recruit talent level was on par with what he and Sumlin recruited as HC.
At A&M, the two preceding coaches recruiting classes were solid top 25, routinely dropping into the mid to low teens, cracking top 10 a couple times. Comparing records, in 5 years Sumlin has won 12 more games than Franchione, or 2.5 games a season. He has done much better than Sherman. He's gotten them to bowl games every season and won more of them than those two combined. He's also coached all his seasons in the SEC, which clearly is better competition, and yes, that means his seat gets hot a lot faster than if they were still in the Big XII.
So he's consistently won more often at A&M against better competition with better recruits.