I really like the concept of "collateral damage" and trying to pick enough forces to win, but not too many to cause excess. However, for players to do that well I think they need more information about what kind of forces they are going to face in the next wave and where those forces are coming from, etc.
I couldn't adequately defend my healers because enemies spawned from unexpected directions. I would also zoom the camera out. The units are so fast, it's really easy to miss most of the action as they dart off screen to fight the next enemy.
Really like the underlying mechanic and I'd love to see it fleshed out further. Game also ran super well, no major bugs I could find which is impressive for a short game jam! Good work!