Google can counter with “All Android devices* have the ability to side-load any app you want”. I did just that with this app.
*I think this is the case
Now if GAB sued Apple, they would have a tighter case.
Except Apple didn’t kick Gab out of their store and usually allows competitors to sell apps through their store if they want.
Also, it is not recommended to load apps outside of Google Play on Android. https://www.wired.com/2016/12/never-ever-ever-download-android-apps-outside-google-play/
Not really because Apple does not have a search engine nor Gab like features.
Their rebuttal will be that the Google action deprived them of the vast bulk of what would have been their normal trade. Google is in fact engaging in a discriminatory restraint of trade.
Google needs to be declared a "Public Carrier" and regulated.