OS fragmentation is an issue only because manufacturera are not updating their firmwares, not because Google isn’t supporting the OS. Apple doesn’t have this problem because it’s the only manufacturer, and you pay the premium dollar to support apples monopoly.
Also, apple has abandoned several iPhone and ipod models, so fragmentation is still an issue.
Side loading apps are not a threat, unless a user takes deliberate action to enable installation of apps not inone of the authorised stores, and then loads apps that are of a dubious nature. In this case, the user needs to take responsibility for their own (stupid) actions.
Apparently apple harvesting is own users call logs and user gps locations seems to have been overlooked.