Thanks for the comments and for playing!
For party-size and difficulty. That got partially ruined by lack of balancing and that bug letting very tough characters heal during battle. It’s true that larger party spreads out gear, but non-participants also get partial XP from each battle. The second way it would have helped is to have more characters to cycle through battling in between visiting the healer-slugs.
You’re idea about swapping party members during fight is on my list of how to increase player agency during battle. I’ll also consider fleeing. Probably giving monsters an attack of opportunity each and then putting them in forced rest-mode for a second or two so that the player really has to run away from the room.
I’ll look into monster movement, my plan is to ease them between tiles too rather than teleporting and that in its own right probably will slow them down some.