I just meant that it's reasonable to make the tradeoff to trust a vendor like Apple/Google/etc. with whom you have fundamental philosophical differences now, if their product is better than the alternatives. What's not OK is to have no possible way to switch.

Changing an email address or phone # is probably enough of a lock-in to be "impossible". Changing the service provider you use otherwise to provide your phone/email/etc., probably a pain, but possible.

Facebook doesn't support indirection (which is why it's crazy that businesses promote fb.com/site urls), but as you've pointed out, it doesn't actually provide a useful service, so if it goes away, no big loss.