Look, if you make it enclave troopers on modified deathclaws and add a little "we ran out of vertibirds justification" or "Power armour requires too much maintenance " it would fit into fo5 without a problem. Fo4 had aliens, the prydwen and synths.
Riding on deathclaws isn't that outlandish in comparison.
Besides, they're one of the few animals that can carry a human AND are fast in the fallout universe. So it even makes sense in-universe!






