Totally valid points, they are noted. I do believe the hit registration issue you have is because of your low framerate yes, since the collision check is activated when attacking and is checking each frame/tick. So it might've been skipping some areas for you.
And as you say, the first thing we'd fix is the progression of enemies spawned. It ended up being a last minute addition and we didn't have time to add extra logic to that. Instead crossing fingers that it wouldn't get TOO overwhelming in the early game ^^