I don't think the attack on Rabble actually does much to make it enginey. Envoy and Smithy can rarely compete with Village strategies these days, so Rabble's attack's stackiness doesn't matter much.
Whaaaaaaat?!!?
You are crazy. Rabble attack stacking destroys big money.
My point was, Smithy stacking usually finds a way to destroy big money -anyway-. Most BM smithy boards lack a village altogether.
But I still disagree with the point you're making. Village/Smithy needs a bit of help to beat just smithy/BM. Village/Rabble needs a lot less help to beat rabble/BM. The attack really does add a lot.
Especially in the end game where forcing your opponent to shuffle more often is about as hurtful as leaving a Province on top. I mean, even if you discard 3 Coppers, your opponent is 3 cards closer to shuffling that fresh Duchy into his deck.