But your gripe is not about open platforms. Your gripe is that Apple iOS is not an open platform. Those are two different things, there are open platforms out there.
My complaint is that iOS as a closed platform is a feature, and Apple has been a good steward for that platform that has made it a stable computing platform for the general public. Corporations (cosplaying as "poor indie developers"), are simply frustrated that Apple isn't allowing them to abuse their users for extra dollars.
These same "developers" who pretend to care so deeply about open platforms don't even distribute their software on Linux. The concern trolling about open platforms is a farce. Picking on epic games again - you can't play Fortnite on Linux. It's "open platforms for me, but not for thee"
Forget the advertising angle, lets look at payments. Apple forces you to use their payment processor and they charge a larger fee. What does the consumer get? They get a single control panel for all their subscriptions that they can cancel at any time. "Developers" hate this - not because they want to charge you less, but so that they can make you jump through 50 hoops in order to cancel.
If I have to choose between two evil corporations, Apple and the greater tech industry that shit on the web, I'm picking Apple. If I care about open platforms, I'll move to an open platform, not lobby the government for Apple to open theirs.