Ok, so why is it a big deal it fires from a locked bolt?
This allows it to chamber larger rounds, like .40S&W. a blowback action in any decent pistol/rifle cartridge would require a considerable spring to hold it in battery while firing (why the little PPK has such a stout spring). I can't speak for the MAC- style guns, but I think they're blowback as well? Correct me if I'm wrong.