I've seen some autoblockers. Even people that are known in the community. It's not hard to spot it considering they follow each feint almost instantaneously.
I mean, that's also just some peoples fighting style, I fight that way (which is why I've been accused of having autoblock sometimes) but I've never seen anyone who I legit believed used autoblock especially not in a duel tournament, so I don't really see the need to take counter measures against it.
No, there's a difference between fast and instant. One of the culprits was called out once and I noticed drastic changes in blocking ability. I'm not like bill that accuses everyone that can block of using autoblock.
P.S. I don't really care, because it takes more than obsessive blocking to beat yours truly.