This game is a lot of fun, BUT:
1.Get to Super Max upgrade 6 or 7 as soon as possible (if you always try the hardest bosses, it's possible in the 1 sector)
2.Activate it right after the end of boss dialogue.
3. Fly right into boss's head.
4....
5.PROFIT!
The boss is dead in 2 seconds. Literally.
I think Super Max upgrade should be a little more expensive.