If the DNR wants to stop AR pistols all they have to do is limit overall weapon length or barrel lengths. For instance if you say that barrels have to be longer than 4", but no longer than 6" then you'd pretty much eliminate AR pistols. Shortest barrel length I've seen is 7.5". I'm sure some moron could also on a shorter barrel, but those ballistics would be garbage.
You are right the ballistics and accuracy would probably suck. There are already 4” barrels out there. Haven’t seen any for the 450BM or 350 Legend yet.