That's really two core things about this. The blue potions you're given at the start are severely underpowered (they only have one use, and the majority of witches are never in a position you can use them effectively) and some of the witches are just hell to deal with. The bovine witch in particular I've only ever gotten past once, using the bovine potions she has against her. But given the potions you get are complete RNG... It's basically not worth trying to face the bovine witch without the bovine potion. If you get to her without it, you're basically guaranteed to end up with a full deck and a guaranteed loss.
It's really sad, because I know there's a good amount of content past the bovine witch... But I don't get to see it, because it's impossible to get past her.