As soon as you get the mint, it's not about hitting the potion, it's about hitting the mint. Before, it's about hitting either of your treasures. Alchs are immune, but they're also on top... which means that they're letting everything which has a possibility of getting hit has a higher probability. So for instance, you get mint on turn 21. There are 19 cards in your deck. 7 Are alchemists, so assuming I am actually playing 4 knights a turn, I hit 6 cards out of 12 non-alchemists. On every turn, I either need to hit all your gold (this turn, it was only 1) or your mint, and you are in pretty bad shape. Now, there's also some chance that I am not actually playing all those every turn, and a small chance you can protect your key card if I hit another.
So, I think you're pretty lucky to have that, but not like obscenely lucky - not too long after this, you have more cards, and very importantly more gold. Of course, hitting potion early would be nice, too, but it's a game.