It’s a well founded worry.
Activitypub represents the lowest dev entry costs and as a bonus it comes with an audience. If Facebook is standing up a cheap competitor just to take advantage the barrier to entry is miniscule.
Given the trouble some users have noted deleting content (erasing also kills your Instagram account), it might also be a play to deprecate a duplicate platform under their control.
It’s a very interesting thought, but it will always struggle to account for variables you can’t see.
It’s always going to be designed top down to approximate your own development as human from the ground up. I don’t douby AI as a feasible possibility, but I don’t think we’re headed for digital clones. They’re always going to have some amount of the creators ghost or assumptions in the machine.