To me I look at the poise in the pocket, decision making, and talent around the two QBs. Did Purdy's teams have the better wins? Sure. No question about that. But wins are not a QB stat.
The defensive performance in the last 4 yrs has been unbelievable. Many big time plays were made by others - Kene Nwangu's kick returns (Bay, OU), Breece Hall has had many big time plays / moments.
I love Purdy and all he has done for ISU and the way he leaves it all on the field.
But....
There was never a moment in a game where we were behind and I felt like, "get the ball in Purdy's hands and all is going to be fine". It was more a hope that the team could make enough plays to win - on ST, Def, and Off. Purdy is a key part of that. That is why he would be #2 on my list of best ISU QB's I have seen. But watching Wallace's poise in the pocket and ability to make plays... Just couldn't wait to see what he would do next. Never had that feeling with Purdy.
Last thing I would add, maybe if the coaches let Purdy go off script for 4 yrs and play the way he did as a Fr/So he would have had more of those moments. I don't know what was best for team success, but many of Purdy's numbers seemed to be better when he was playing outside the system / off schedule vs. within the scheme.