I also find your excuse-making amusing...

1 - "Williams fumbles"
Yeah, heaven forbid that USU's defense had anything to do with the fumble and recovery. Silly JSwagg just beat himself...
2 - "Taysom driving fairly easily for the score"
BYU was on the 50, and it was second and 7. Taysom's run was bottled up, and BYU was going to face a long third down regardless of whether he got hurt or not. Point being, that drive was stalling, even with Hill in the game (https://www.youtube.com/watch?v=xaP2qim8wGU)
3 - "USU throws pass over the top"
Yep. That was because USU was running a very effective max protect blocking scheme, and their WRs beat BYU's DBs

USU's defense also came to play. Even with Hill in the game, I think USU still wins. BYU's defense didn't have an answer for USU's max protect passing, and USU was leading - even with Taysom in the game.

But if we're going to play the injury card, it should be noted that the Aggies were also playing with their backup QB... If you're going to indulge yourself by imagining that Taysom stayed in the game, you should at least be consistent and imagine that USU had a healthy Keaton.