I’d say both yes and no - Apple’s now booming services division (which includes the App Store) only started to produce meaningful revenue and profit after introducing a range of ancillary and subscription services.
Absolutely agree that any change to their business model will be a hit on their revenue - but I believe people may be grossly over stating how much of Apple’s services division profit is coming from that 15/30% share. Running the app store is easily their most costly service and stable users aren’t in the habit of buying apps - but those people sure are paying their monthlies on iCloud/storage and music. (Also not to forget that apple get a cut from every Apple Pay transaction.)
b) It's under scrutiny but the legal consensus being formed is that Apple simply needs to allow links to alternate payment systems. It doesn't need to allow sideloading or offer alternate app stores.
c) Some countries are looking at forcing Apple to offer a "choose your phone/mail/calendar app" screen on initial phone purchase which does have precedent and looks far more likely.
Well, their contracts with AWS should expire in a year or 2. Also, they've used AWS, GCP, and Azure.
It only makes sense to migrate to their own cloud.
They're already offering Xcode Cloud. The logical step afterwards would be a public cloud. This is where the big money is.