It's a problem of pacing and balance I think. The game needed to escalate it's difficulty at a better pace and place smaller difficulty spikes throughout. As it stands the only real pushback the game gives is asking you to face the bosses forms back to back.
Even setting aside my mistake I don't think the game adequately prepares players for the final encounter. It just never asks you to understand or accel at the games mechanics before that very last moment.
benpack's comments