Surely the biggest threat to the forward austere base CAS as provided by the F35 is a range of rapidly maturing precision guided ground launched weapons.
I think during the conceptual development of the F35 things like GMLRS, Excalibur and guided 120mm mortar rounds were not around. Now we have those, plus loitering munitions and various UAV's the need for CAS gets less.
It will never be reduced to zero of course but the fact is, for putting explosives onto the heads of enemies, the USMC, and of course everyone else, has many more options.
I still think the austere basing capability is an important thing to retain, flexibility is never a bad thing, surely?