Definitely could save a couple of frames by collecting two comets faster. Likely there is around 10 frames to be saved on each boss fight with better timing on the shots.
Likelihood of using other weapons is low, Cannon or Hammer are best ones, Wide could be considered due to spawning 5 bullets, and killing bosses faster BUT it is so BAD in all other scenarios, specially in bosses that have lots of parts to break first. Side would be ideal for the side boss fight but, to get it and then change back to something useful is too slow.
This game is too niche for me to even WISH for others to TAS it, or come talk to me about it, BUT, it would be fun to do on the side, specially if I get someone to optimize it with me. Also my first TAS ever, lacking lots of knowledge for managing the TAS Editor, that was kinda of a pain, I hope to learn soon...