What are the mystery drones flying over the US?

One concern I have is that this gives the FAA ammunition to further limit hobbyist/recreational drones.

THAT is your concern here? Brilliant.

What should the concern be? Imaginary Iranian motherships?

Their real component at minimum

All the videos I've seen looked, moved, and sounded suspiciously like helicopters, complete with blade slap.

A short article that only answers, "we don't know."