oh ho. an expert--that's a good one! did get into dominion a little back in the day, but I don't do much with deckbuilding in my own design practice, unfortunately.
some final thoughts. did one last playthrough (it's fun!). was able to farm the positive feedback cards (I think there are two? 'raging edge', which quickly spirals out of control, and something something blade) pretty successfully. it looks like one of you may have capped the total mob count to ~20, or at least it seemed that way, since some squid thing just flat out stopped calling for reinforcements. by the end of it all I was dealing about 400 damage per turn.
there are many ways to combat this kind of thing. slay the spire I think features several enemies with positive feedback loops of their own, making lingering in encounters incredibly punishing. you do a little bit of this with the shield buff squid. but really you might just want to apply reinforcement actions more delicately, and pair them with powerful opponents (which check the player) rather than making it a thing you can always just do.
I'm definitely not against easy trashing--it can be a powerful creative tool for the player. but perhaps if you go down that route, you might consider balancing it against something else. all roguelikes sit somewhere on the control/constraint creativity spectrum, right? i.e. whether you're forced to play the hand you're given (pun intended) or you have the flexibility to always make your own build, no matter what. this has apparently been described as 'headroom' in the past: http://nethack4.org/blog/strategy-headroom.html (kudos to my jam partner Elliot for sharing this with me recently). what I like about shroom & gloom is that the cards feel more component-based and buildable than the typical deckbuilder, but maybe you're not trying to move in that direction. I mean, if you don't, I will! :)
speaking of which: it seems as though there are no tradeoffs to all the stacks you can put on cards. one common strategy I had, which feels degenerate, is just to load everything useful on one uber card that I know I'm never going to lose.
finally, here's a dumb thought. I realized that you guys are one key away from a mouse-only game. don't get me wrong, the W card is gorgeous, but if I could just click to move forward I could throw my keyboard away and put my feet up. the ultimate lazy day.