Haha! Having the "W" to move forward (rather than a click) was the closest we came to having an argument during the jam. I think we could probably include an option for people who want to play single-handed, but there was something about pressing forward that felt a little more visceral.
We're not big fans of puzzle games, so I think our natural instinct is towards more headroom, more viable strategies.
That said, the thing that bothers me most about more headroom designs, and is mentioned in that pretty excellent article, is that players will repeat themselves given the chance, and this is boring. You mentioned headroom in the context of farming strategies in Shroom and Gloom, which is something specifically mentioned in the article, though the solution the author found probably won't save players from their min-maxing instincts in Shroom and Gloom.
Sorry if this is turning into a bit of a long response, I'm just interested in thinking about aethetics-of-dynamics in deckbuilders.
Despite some divergences, Shroom and Gloom is a "Slay The Spire-like" (which is a genre these days, one that I'd prefer to call a "Dream Quest-like" but that game never got popular). And in terms of the headroom dynamic, these games have a lot going for them. As in, they avert some of the problems of too much headroom simply by not giving many options (in Slay The Spire-likes the first choices are all "Choose One Of Three"). (in this way Slay The Spire-likes are quite different to traditional Roguelikes).
Alex Smith (the author of that headroom article) would argue that limited card choices steers players due to the low headroom in subsequent choices, that the player has to commit to a path once they've chosen it. He'd be right... but there's still something curious about simply not giving players most of the choices in the game. i.e. it's possible to make a game with relatively high headroom, but low repetition just by having a lot of content that doesn't appear every run. Like simply not offering any cards that allow farming is an actual solution, even if these cards exist in the game and do appear sometimes.
And the thing about CCG's in general, is that the random-draw-from-a-deck is naturally great at getting players to improvise (which is the opposite of the feeling Alex Smith identifies as being caused by too much headroom, i.e. Players deciding on a strategy early on and then just sticking to it). I feel like there's got to be a way to disrupt a farming strategy through introducing more randomness, like if the first half of a run involves a lot of farming, but then some event takes place half way that provides an even better approach, that would reduce the overall repetition, and as I see it the repetition itself is the problem.
All of this is to say, that I feel like Shroom of Gloom is in a good place with its headroom... but there's consequences of our highish-headroom approach that you've pointed out that I'd like to avoid - like repetitive farming, and low improvisation decks (that have few cards, and so more repetition when playing).
And I desperately don't want to reduce the headroom to solve this by direct nerfing of options (which is the low headroom approach), while I also desperately want to limit the boring strategies.
What's left then are largely content-based solutions. As in, solutions that involve more content that introduce new incentives for players or otherwise force players to improvise around a new element. And I suspect in a high-headroom design paradign content is usually the tool that solves problems.
You've already mentioned some approaches with limiting farming, like new enemies that gain in power. My feeling is, whatever these limits are they need to be baked into the rules of the base game, rather than specific encounters. For instance: all basic enemies can flee (after a turn or two) when they're feeling doomed, but then come back in a later fight. The same amount of killing enemies for "If Fatal" improvements might happen, but it would be less possible to ignore enemies and keep buffing your cards (which isn't a fun strategy).