IMHO piston setups are good when running dirty ammo and you want to keep crud out of the action. That's why 5.56 ammo usually burns clean since it's probably going in an AR. But I run steel 5.56 and a LOT of dirty 7.62x39 in DI ARs, no issues. And an AR is pretty easy to clean.
I don't care for piston ARs, more reciprocating mass, too expensive. There's plenty of piston rifles out there that work fine.