You are right.
The problem when I developed the spawner system I didn't take account of interruption (skip wave if core is not there), I had plans to do that, but there was other bugs needed to get fixed.
This was my first attempt in developing structure building system and simple combat system . My most focus was in making the player fun and smooth with the limited sprites we had. I wanted to have special move for the player too, but there was not enough sprite for the character.
I'm glad you enjoyed it.