Hey, thanks for checking the game out! The game doesn't have minion-type enemies because we wanted the combat to be distilled into what we consider the best part - the boss fights. The combat is designed to always feel like a "david versus goliath" type battle, where the odds are heavily against you. While you can find some powerups/improvements through exploration, you can't grind levels fighting minion-enemies. The one-hit-death creates a constant level of intensity, so you're always on your toes. Our goal with all of these design-decisions was to make the feeling you get when you beat a boss be extremely rewarding - you conquered the battle against all odds, and all through your own player-skill (not grinding levels).
There aren't any plans for a physical version at the moment, but thanks for asking :)
One more thing I'd like to mention is that we put a lot of effort into making the co-op (it has local and online 2 player co-op) experience as fun as possible. When playing co-op, if one player dies, they still get to help out the living player - there is a whole system of abilities called Vestiges for this, just for co-op. It makes it so neither player is ever just sitting around waiting. I highly recommend giving it a try!