Hey!
Sorry for the late reply, I've also been busy with other work but I really appreciate your in-depth comment and review!
On the topic of level design, I had to cram in every single level around the last hours I had working on the jam. Due to this, a lot of the middle levels were especially rushed as I just needed levels/content for the game. Thus I resorted to making those areas a lot harder than they should've been.
If I spent more time on the level design, I would've 100% geared the game towards more puzzles like the last level. It especially sucks to see in hindsight as most people generally quit playing after the platforming bits due to the difficulty, and don't get to see the last puzzles.
As for the features and mechanics that got cut, I've actually forgotten a lot of what was originally planned since it's been a while. There was this main concept of electricity puzzles, mechanics letting you chain currents together to complete circuits and power objects. Even the idea of a robot-type character that could aid in the electricity mechanics.
On top of that, there was also the idea for enemies in the game, which only a specific fighter character could kill with a weapon. Even small quality of life features like a character selection wheel to make switching less of a hassle.
Honestly, a lot could be added upon and improved in this game. For example, the voice dialogue/banter between each character you mentioned was a great idea.
Thanks again for going out of your way to leave a review/comment, I'm honestly surprised this game is still getting minor traction.