The argument that BYU beat a great Pitt team is pretty weak.

To summarize, Pitt was #18 the previous year, but had talent coming back so ended up preseason ranked as #3. But then BYU beat them and so their morale was crushed and THAT'S why they finished 3-7-1, but BYU still deserves credit for beating an elite team. I don't necessarily buy that.

For me, the biggest argument for why it has to be BYU comes down to "Who else?"

Oklahoma St finished 10-2 with victories over only 2 ranked teams but losses to both Oklahoma and Nebraska.

Nebraska also had 2 losses, including one to Oklahoma.

Oklahoma had 2 losses and a tie...if they'd beat Washington in the Orange Bowl, they might have had an argument, but they also lost to Kansas (who was marginally better than they are now, but still had a losing record)

Washington beat Oklahoma who beat OK St and Nebraska and is generally the 2nd option, but only played 2 adequate teams besides Oklahoma - the same Michigan that BYU played, and also USC...who beat Washington. So their schedule was pretty close to on par with BYU's and they had a loss.

Florida had some good wins (and modern analytics suggests they might have been the best team), but they also lost their opener, then tied in their second game and weren't eligible for the postseason anyway.

Bottom line? There wasn't a great team that year, but BYU was best of the bunch...which is what defines a national champion.