Glad you enjoyed our game!
I agree, we could've done a better job with the waves. The reason why enemies are introduced at a slow pace towards the end is because they originally didn't exist when the rest of the waves were created. For example, the golems were introduced in the final day of the jam.
We experimented with pressing a button to dig holes, but we weren't sure how unity would handle collisions when 2 objects are placed in the exact same spot(something possible with having to press a button, but pretty much impossible when you have to move the mouse). An early bug where the waves would sometimes end before all of the enemies were defeated(meaning your holes would be erased) made us scrap this.
I agree with the other ideas. Thank you for trying our game and for the suggested ideas!