Thank you for the very detailed comment! I'm glad that the core of the game is actually good.
From what I understand, many problems are related to just tweaking numbers, it shouldn't be that difficult to fix.
Regarding the waves logic you're completely right, I got a bit overwhelmed :3 Yes, the waves are groups of enemies, and those groups get randomly spawned. This way you get a fresh run every time and I hoped to keep things fresh a bit longer. I already have plans on how to improve it though, since some groups as you said are not well built.
I will definitely pick it up again for balancing and smoothing things up, that's for sure.