I guess it'd be pretty easy to optimize from a TASer's standpoint, but it'd still be cool to see

I don't think it will be interesting to see because it will basically one shot every boss. The game can probably receive 60 keys per seconds (or more) so a single phase takes like 1 or 2 seconds.

Update: I've made a All Bosses TAS:

It’s wild how fast the TAS goes, I wonder if the Dreamcast version can accept keyboard inputs that fast as well

Nice, cool to see even if it isn't especially intricate