The USAF is going to have plenty of F-35's to spare, and it it can carry standoff munitions for CAS, not unlike light attack aircraft which you aren't going to be placing into direct line also.
The A-10 was designed to take a beating, it has redundancies on top of redundancies, and armored cabin and fuel tanks, you can blow half of it's tail and it will still land (tho an F-15 has landed with 1 wing ;)).
Light attack/trainers are OK but they aren't in the same league.
But is too expensive to ever risk danger-close. Whereas A-10's have had mortars fired over them in certain circumstances...