I don't play much anymore.But I think if you want to have an infusion of new blood people need to cut down on using deadballers.
Newbies are prepared to lose.But when they can't even hit homers,that gets them too frustrated

C/A+-D/A+ defense is what I focus on when I’m using modern pitchers. It seems to work pretty well - have done OLs or themes in awhile though

I think one advantage of deadball era pitchers is that you can exploit your offensive bench more. Higher IP leads to running fewer pitchers which lets you have a larger bench on offence. Since you required identical offences you couldn't exploit this in your test. I thought the main advantage of deadball pitchers is that I can play something like 7-9 pitchers (3 starters, 1 LR, 2 setup, 1 closer, often a second LR, sometimes more) and 16-18 batters which gives me enough people to put the entire bench on if I want to save ABs on my core team. That's a lot nicer than the 10-13 pitchers (5 starters, 2 LR, 2 setup, 1 closer, sometimes more) that is more typical of modern pitchers where if you decide to (lose a game/play entirely bench) you only have 4-7 players to put on from the bench and have to use up PAs from 1-4 of your core guys in a game where you don't want to (with 5 bench starters your chances of losing are quite high so it isn't great to use up core appearances). Overall I think you can get away with lower PAs on your offensive starters when you run deadball pitchers, which means your guys are better in games that matter. I do agree if you don't get extra bench slots deadball and modern are nearly identical in performance.