Being a monopoly isn't illegal. So many discussions gloss over this fact, and people get at each other's throat over hypothetical abuses and ad-hominem scenarios.

Abusing a monopoly is illegal. Alphabet and Apple are both unquestionably monopoly businesses, and make incredible year-over-year revenue through market-damaging services like AdSense and the App Store. If they are allowed to continue, then other Fortune 500 businesses will copy their decisions, thereby destroying genuine market value that they provide in exchange for safer, more exploitative revenue streams.

In the case of AdSense and Apple's App Store both, I think that any fair FTC investigation would conclude they are shakedown services that harm the greater economy.