How much of the 30% did Apple reinvest back into developers?
The problem is that you have no idea. Developers have *some* idea because we literally can see the benefits of the 30% first hand.
But if you took some time and do some research, you can make estimates from their financial statements and reported numbers.
If you want, I show you my math and sources (it's a long explanation so I'm not going to write it all out unless you want, but I doubt you're going to read). It turns out, Apple in 2019 made about $15 billion in revenue from the App Store cut and I estimated that about $5 billion is reinvested back into the developer platform.
Now, 66% margin is a nice fat margin, but compared to Android, I suspect Apple is investing far more than Google back into the platform.
On Android, Epic *can* already run their own store on Android but they're currently failing to get adoption because no one wants to install it. So asking for a separate store is unlikely to change things as we've already seen, what else does Epic want? Asking Apple to decrease their cut to, let's say, 20% would essentially cut back investments into developers since Apple knows they're ahead of the game in developer side. Cutting back investments is bad for small developers and 80% is only going to benefit large companies.