I believe this is actually only true under very specific circumstances -- namely, enterprise certificates, which are used to distribute apps directly to employee devices, without going through the app store. If they decide to revoke a regular developer certificate, the apps already distributed through it are not affected in any way.

They can control which apps can and cannot run as long as those apps are intended for internal use by enterprises. That seems reasonable imo, given that these apps are also not subject to any approval process.

No, they can control what applications are allowed on their app store and control how the OS they distribute runs. Aside from those two things they can't really force anything that you haven't already allowed, or continue to operate.

Apple can't physically confiscate the phone or the data that you put onto it's hard drive (not talking about iCloud). It's yours. You can put linux on your iPhone if you want and there is nothing Apple can do about it.

On Android, one can sideload an app. Amazon has it's own app store. Chinese Android phones have their own. Android was initially designed with this kind of openness. In fact, Google didn't have an app store initially. Now, there are pros and cons to these approach. FB could be side loading Android apps all day long, doing who knows what, and there is not much Google can do about it. Now, if they were a bit smarter, they could've used a shell company's throwaway certificates. I cannot fathom why they would do something this shady using their own corporate certificates.

Yes, google has no excuse not to know better. They did know better in fact, it's a selling point of their competing product. Corporations their size will typically run anything remotely important in house on their own machines so that they have control over it for exactly this sort of reason. Failing that they'll put contracts in place that specify notification periods and remediation steps so that the rug can't be pulled out from under them. Google knew this could happen and went ahead anyway, they accepted the risk and now they have to accept the consequences.

And let's not forget that google weren't working with apple, they were working around them.