Wow, your kind words really mean a lot to me! Particularly coming from one of the developers of my favorite game so far this Jam!
You caught us! The main secret to succeeding with our game is definitely "draw bigger circles!" Sometimes it feels like a cheat code, haha. So we definitely didn't nail the balance of the game, but on the other hand, it seems like many of our players didn't discover this trick, so we probably could have telegraphed it more, maybe through more careful design of the first boss.
You must have fought Nullframe "Neon Oblivion" as your final boss! He was designed by one of my co-developers, and he is easily my favorite boss in the game. I'm glad you got him as your random selection. Great idea to take his Corruption spawning ability and add smaller versions of that to the other bosses, that will help balance the "draw bigger circles" strategy.
Thanks again for taking the time to play our game and share your detailed feedback. It really made my day! Lots of respect for you and your teammates.