Utah/BYU can believe they WOULD have won the national/conference title if given the chance. And there's even some chance it is true. But it's not what happened.
In the past, when there was more ambiguity about what defined a national champ, Utah probably could have with a similar season and with some 'recognized selectors' choosing them, but by 2008 the process was pretty locked down and clear.
I will take a moment to note that Utah (unlike UCF) doesn't actually claim a national championship, though the PAC12 lists it on their site, so small credit to Utah for that