I used a controller, I didn't try it with a keyboard. I don't play these types of games so my suggestion could be shit, but a thought that sprung to mind was to have the robot's ammo limited and replenish based on a timer (but honestly that wouldn't change my strategy, it'd just make me kite for longer).
Best of luck with whatever you come up with, I'd love to see a full game around this in the future! Some game progression would get me better acquainted with the other abilities and make me more likely to rely on them instead of just the one.