It's not just about the engines able to accept an X amount of FOD. Self sealing fuel tanks, EMP protection, and other mechanical/backup redundancies are a factor. I can't speak specifically to the F-35, but other airframes have a lot of not-to-sexy things on them that make them survivable in combat.So much for "battled hardened" airframes.
Shameless self promotion:
The AF security Forces are, ummm not special... so much dumb walking around during this dog and pony show.