The Romans didnt have B-52s or A-10 Thundebolts.
If they did we'd all speak Latin.
No, the Romans did not have those things. But in their day the Legion was the same thing. Ask Phillip V of Macedon or Antiochus IV of the Seleucid Empire.
My point is that the barbarians did not have them, either, nor could they replicate them or operate them. If the barbarians overrun the United States, a B52 will be to them the same as a straw and wattle "Cargo Cult" C 47.