it isn't entirely about if it would help more or not, it is more about giving coaches more control over their rosters. I think some coaches would be hurt using too many redshirts. You mention the trade off Katz, but I think the trade off is inherent in this case. Redshirt more players and you have less to use immediately hurting your chances of winning now. Redshirt less players, and you have more chance to win now, but less later. This balance would have to be determined by each coach. With stamina being reintroduced, each and every player is that much more valuable now.
I can't speak with any certainty about the spread of player ratings, or how it would impact different divisions. I do know that some seasons I would like to redshirt more than three players though. You can't redshirt everyone you recruit every season. That would presumably lead to losses which would lower vision, and allow teams with less talent to win now which would raise their vision. I think most coaches would use the redshirts based on their rosters and recruiting classes, not just as automatic. The automatic 3 redshirts we see now are at least in part the result of the limitation currently imposed.