30% from app stores is the norm for app stores that have market power in their respective markets, but all that tells you is that's the amount of the monopoly rent. Compare this to the Microsoft store, where the store itself doesn't have market power, and then they don't take 30%:

https://9to5mac.com/2019/03/06/microsoft-store-revenue-share...

But still 30% for XBOX/games where they once again have market power in that market.