Your coordination mechanism is to just to rely on the good will of a single company. How long do you expect it to last before apple starts cooperating with invasive parking apps, banking apps, etc?
It is a little rough. On reflection, the scenario when apple would sell you a locked down phone and google would sell you a side-loadable phone was ideal- the locked down phone was in my opinion better for phone tasks, but apple couldn’t abuse that too much or I’d just switch to android. A scenario where everyone is selling locked phones could remove that necessary check.
