After a couple more runs with the low nodes deck on the mystic... it might need some uptuning on some of the numbers. Not 100% certain yet but it feels kind of rough at present. The mystic's unique mechanic is really fun though!
I've finished a couple of runs with the defensive deck on the mystic, and it feels really solid. I'm still getting used to drawing the extra patterns and making effective use of them, but it felt easier to win using the defensive deck on normal than to beat the first boss (and I tried 3 different options) on easy with the low nodes deck.
I'm not certain how much of this is an actual balance issue, and how much is just that this game is harder on a touchpad, though xD