I think your opponent made a mistake trying to go Alchemist at all. Surely the better strategy for him is to commit big time to a Torturer/Native Village engine that draws his whole deck without having to dip into a Potion-cost card at all?
This is a good board for Alchemist (+buy, trashing, Colony), and perhaps Alchemist is the dominant strategy. In which case I don't think pursuing them from a 5/2 start was going to work out for him.