The problem with this argument is that Microsoft doesn't sell anything on XCloud.
Yet.
Disney+ started out a a streaming service, but has since moved on to transactional video on demand with titles like Mulan and Raya.
Because it’s not difficult to see these services potentially becoming App Store replacements one day, it’s understandable that Apple be more cautious with them in the short term. Especially considering how App Store vitality and viability is important to both Apple and its users (more on that below).
To me at least, it makes more sense for Apple to be more cautious upfront (and then loosen up later on once things like revenue share agreements have been ironed out). Rather than let them flood the App Store like no tomorrow, and then trying to manage them afterwards.
You don’t become a trillion dollar company by being laissez-faire about this sort of stuff.
Why does Apple give a damn where people get the games they are playing? If I wanted to subscribe to Apple Arcade, I would - but because I don't want to subscribe to their model, other developers need to jump through hoops to get content to users? When will the same thing happen to Netflix, Amazon, Hulu then now that there's Apple TV+?
As I said above, it’s more about ensuring the continued vitality and viability of the App Store, and less about staving off competition for Apple Arcade.
I maintain that the App Store has been a good thing for the majority of developers, especially those who don’t have brand recognition with consumers. Notice how it’s all the big-name companies like Spotify and Epic who are going after the App Store? They know that if they don’t act now, it’s pretty much over and the iOS App Store will become the law of the land.
It is really in Apple, and its users’ best interests that the App Store not be positioned as a loss-leader (viability), hence the current paradigm where the 30% cut from the larger developers goes towards covering the costs incurred by the majority of smaller developers who earn Apple next to no money.
At the same time, you don’t want customers being pushed out of the iOS App Store (vitality) because then that means fewer people spending money on apps in the App Store.
Being cautious isn’t illegal.