I really appreciate the honest analysis and feedback! I really agree with everything you said. We we're actually planning to do an upgrade system like you said at first, but because of the time constraints we we're forced to just give everyone all the abilities at once.
I think that sacrificing the player experience for more content/graphics might've been an issue though, because of the reasons you stated. No matter how good our balance or mechanics or graphics are, if the game is difficult to play or get into then the players will be frustrated and less likely to have fun.
(Nobody has beaten wave 10 yet, but so far you're the first to make it to have 9 and see the OP LASER BEAM SLIMES (did you try the cool hint owo?))