Currently playing the demo (v1.6.1). Really enjoy the game!
I though of simple quality of life feature that I think would be easy to implement. When trying to optimize fielded units, I often found myself splitting the units (shift+drag) to be able to transfer the correct amount of units I want to field to reach the max unit power. One easy improvement would be to automatically match the amount of units to reach the max power when dragging a unit type from reserve (e.g. with shift+drag either split the stack in two when half of the stack do not exceed the max power or split to max amount of units to reach max fielded power). I hope my explanation is clear.