Adding more damages to the boss' bullets would indeed balance this playstyle, but the problem with this game is that it was impossible to balance all the powerups combination perfectly, during the 48 hours production time. I like the idea of a boss that is pretty easy to kill once you've find the strategy to use, but here it is a bit too easy to find its weak point.
Thanks a lot for playing and taking the time to send me your feedback, I appreciate that ! :)