And making hardware “software agnostic” you end up with the crap like Android and Windows.
There is a reason that consoles exists - where the hardware and software are integrated
How come? User doesn't have to buy an iPhone. Many buy Androids exactly because Android has some apps that they want, so not only it is a competitive market, but it's also a market where this exact issue (whether certain apps are available) drives (in part) user decisions.
[1] it is not just the number of iPhone users: if you don’t go to iOS marketplace, your sales on Android may also be impacted.
I've been making mobile apps and games for a long time, and this is completely untrue. Developers choose a platform, Google play, iOS or both, very consciously. Other, smaller app stores (based on Android, mostly) also exist. If Google Play radically decreased it's fees, it would actually make a lot of developers to choose Android first.
The fact that it's rational for developers to release their apps on iOS doesn't mean they have no alternative or Apple has a monopoly. It just means it's still better for them to release on iOS than not, even with these fees. Microsoft it's not worth it for them is exactly how free market works. If some users want this cloud gaming enough, it will influence their Android/iOS buy decisions.
This would be true if not for bundling.
Lets say users care about A, B, C .. all the way to Z. Apple makes G really suck, but do the others well and bundles everything so you have to purchase all of them together, now a competitor can't just go in and make a batter G they have to make a better A, B, C and everything else. This is typical anti competitive behavior and result in companies just seeking rent rather than working hard to compete and innovate.
Apple stores sucks because of this, it is really really bad compared to competitors on other platforms like PC, steam is a massively better product since users choose steam it isn't forced upon them by the computer creator.
This may not be true for your business model because your product seems to be an app, but it is not „completely untrue“. Many businesses build apps merely as an interface to their product, but the product is something else. They cannot afford losing significant part of their target audience by being picky. They have to eat the costs and terms of all major stores and pretend to be happy about it. The main complaint about Apple is this one: you have to go mobile to support your sales, but you pay incredibly high tax on that.