I see what you're driving at, but I don't think that we can have both sets of gear. Our "fighting the Chinese hordes" gear will work in COIN. Our COIN gear will not work against the Chinese hordes.
It would be great to have both, but that isn't what we buy anymore. We buy the "does it all, but not as well" package.
I would LOVE to fly an OV-10 in Iraq or Afghanistan. I'm not throwing stones at its capabilities. I just don't see it happenning.
So you're approaching it strictly from a budget viewpoint. That's definitely valid - Christ knows DoD lets budget drive capabilities, not the other way 'round as it should be. But I don't think it's necessarily true that we can't have both. I mean, seriously, how many AT-6's could we have for one or two F-35's? Yeah, yeah, I know that's not how it works, different pots of money, etc, but still.
Seems like we need to be developing weapons to fight the wars we're in now. And yes, you can adapt and train a fast-mover for FAC(A)/COIN, who knows how we'd be able to use a Super Bronc/AT-6?
Besides, who knows exactly what we'd need in a war 10 or 20 years downrange? Look how they adapted the Hoov and Tomcat once the FAD and outer-zone ASW missions were devalued. Look at all the oddball missions they found for the OV-10 when it was still in service. Just for instance, rig up an ISAR on an OV-10 like they put a SLAR on the Army's Mohawks. Add in a good MIDS, and I can think of a dozen neat ways to use that even in a conventional conflict.