You're looking at it through the wrong lens. Do you think Rex Grossman is a spectacular player? Would you name a street after Rex Grossman if he did what he accomplished at UF instead of UT? Grossman had 77 TDs in three years. Manning had 12 more with an additional year here. Manning has not earned what the program and vast majority of fans bequeath him.
You are contextually so lost it's incredible.
Before Manning the career record for passing was Andy Kelly with 6,397. (Manning gave us 11,201. Not just a TN record but SEC record at the time)
Before Manning the number of 3k seasons by a UT QB was 0. (In fact to this day there's only been 4, 2 by Manning)
Before Manning the career record for TD's was Shuler with 36. (Peyton had 89, 2nd among all SEC QB's at the time)
Before Manning the most TD's in a season was also held by Shuler at with 25. Manning had 36.
Before Manning the number of 400yd games was 0. He had 3. (not counting a 399)
Any of this sinking in? Manning was an absolute watershed player for UT.
So now that context I've been talking about. You heard of Fun 'n Gun? That was Spurrier's doing. In stark contrast to the above:
Grossman not only isn't his schools all time leading passer but 2 players had over 9k in yards.
Before Grossman the 3k season barrier had been broken 5 times by 2 different players.
Before Grossman there were 6 players with at least 39 career TD's and 3 with over 60. Grossman isn't close to Wuerffel's number either.
Before Grossman Wuerffel had more TD's in two different seasons that Grossman would ever have.
Before Grossman there were 4 3k seasons by 2 different players.
Before Grossman there were at
least (I say that because I'm only looking at the top 10) 7 games of over 400y passing by 5 different players.
So what we have here is somebody playing at a school (and really coach, Spurrier) that really lent itself to passing production. It's kinda like rushing yards for Wisconsin. (Their #10 career rusher would make the top 25 in our whole conference.) One shouldn't diminish what Grossman did but he damn sure didn't blow up his position compared to those that came before him.
If you wanted to do something useful with this comparison (not that I think you could do so without total bias) imagine what Manning would've done under Spurrier with Grossman's teams.