Thing is, youre still leaving him with a 2 card hand. That's enough for KC-something. KC lab, or governor, or scrying pool, or hunting party, or maybe golem, let him play on completely normally. KC any cantrip gives you enough cards to start up an engine, at least. KC any gainer or plus buy restores the same number of cards which got destroyed, and might end the game on cheap piles pretty quick. And you're trashing bad cards for him.
I bet the opponent can set up a counter pin AFTER being pinned himself. And you have obligingly trashed all the filler from your deck, so a single hit on you destroys your pin and your whole deck. Unless you keep around not just one, but many extra villages. Or even then.
I'm sure this can be a good strategy, but it's not as unstoppable as a pin that leaves you at a zero card hand. You have to either catch the opponent off guard, or go over the rest of the kingdom carefully to make sure that it's appropriate and doesn't provide a convenient escape via kc.