Sadly with Facebook,you can't be sure they won't install a backdoor application that will reinstall it after you uninstall it. That may just be some phones with Facebook and Messenger preloaded though.
Yes you can be sure that they’re not doing that on iOS.
It would have to be something preloaded, and with unusual privileges. Otherwise, it isn't installing anything silently on Android. I don't think this would happen at all on iOS.