Um, so an extremely successful and great coach wins a national championship, has a losing season and suddenly becomes as inept of a coach as Kiffin and Dools? Wow dude awesome logic. Since Brown is extremely similar to Fulmer, you are basically saying Fulmer is as inept as Dooley. And Chizik didn't win a NC, Newton did.
Interesting that you point out that Newton was the reason for Chizik's national championship, but fail to mention that Young might have had a hand in Brown's. In fact, the only BCS title game where the team with a lower talent average won was Brown/Young in 2005.
Chizik's team had better recruiting averages than Oregon. About 90% of the time, with the lone exception being Brown/Young, the team with the higher talent average wins a BCS championship.
So if you want to use Newton as the reason for Chizik's success, perhaps you should write off a national championship, some conference championships and about 30 of Brown's wins to Vince Young.
Moving on...
While there are similarities between Brown and Fulmer, let's talk about the differences because those are key when distinguishing one from the other. See the attachment below.
Look at Mack Brown's recruiting versus both the BIG XII and the nation. Since his loss to Bama in the national championship, his talent has continually increased to averaging tops in the BIG XII and top 5 in the country. In that same span, (2010-present) as his talent should be increasing, he has lost 18 games. In 3.75 seasons, with better and increasing talent, he has lost more games than than he did the previous 9 seasons combined. This is what makes him the biggest under-performing coach in the nation.
The threshold to getting fired for under-performance is 4 games below what your talent predicts you win (See: Dooley, Kiff, Chizik and likely Muschamp). As Texas has tops talent in the Big XII, only about 1 loss a season can even be explainable (arguably that loss should come to Oklahoma). That means he has broken the 4 game threshold below talent 2 of the past 3 years, and with four losses last year (if you discount one as just bad luck, see Saban) he was perilously close.
Find a coach who has been allowed to under-perform by those margins in the nation. You will be looking for awhile.
Fulmer, whose recruiting showed a downward trend, with wild fluctuations, performed about as talent would predict (along a downward arc). The SEC's recruiting rose in relation to UT as Fulmer's ability to get talent dwindled. This is almost an unrecoverable state of events, but at least is explainable as talent=wins about 70% of the time.