It's not going to be a few apps and they might not even be a few stores. It's going to be a bunch of stores with varying rules and conditions and bars for quality and selection of apps. I'm not interested in that because I don't trust other companies to do the right thing. If you're interested in that, you can use Android. No one is forcing you to use iOS.
Also, there is no reason to believe any percentage is too high or too low. 30% is what Apple has charged since day 1 when it had no position whatsoever. You will need to explain exactly at which point in time 30% became problematic.
I think it's getting obvious that the situation is untenable. If it's not the US courts, some other court will likely enact changes.
In the end it doesn't matter how Apple and Google got to this duopoly position of power, if it was fair or of they had to work hard. The fact that matters is where they are now.
Also, there is no reason to believe any percentage is too high or too low. 30% is what Apple has charged since day 1 when it had no position whatsoever. You will need to explain exactly at which point in time 30% became problematic.