We (in this case the EU) should give it the same treatment we gave credit card companies. Cap their rates at 1% or whatever so they can cover the operational costs of their stores, stop them from banning apps from their stores that aren't breaking any laws, and that's that. If they want to make more money for their shareholders they should actually build things rather than abuse their gatekeeper position.
Just imagine if Microsoft had taken a 30% cut from every developer who ever compiled software for windows, or told them what software stack to use to develop their software. We'd have gone on the barricades immediately. Microsoft had to face scrutiny for bundling a browser, compared to what smartphone companies have done to their devices that was a joke