I think that so much goes into QB play that it's hard to tell whether anyone really regresses. What's the running game look like? Who are the WRs? How is the protection? People will say that Sam Richardson regressed at ISU, but he took so many hits that he was understandably a little gunshy.
Purdy started his career with Butler, Murdock and Jones...that is a very strong college WR group. This past year, he didn't have as good of a group and a lot of that had to do with Milton getting hurt. But, the TE's stepped up and were great. So, his overall stats weren't as strong, but by the end of last year, he was playing at a VERY high level. We get that Purdy and the sky's the limit for this ISU team.
I'm not going to weigh in on the iowa QBs, as I don't watch enough to know what's going on around them or even what that staff is asking them to do.