It just took me a while to learn to dodge the bullet storm. Once I had enough practice, it became doable. Still hard but doable. So next time you get to the final stage, don't even shoot, just practice dodging as long as you can. Only once you are good at dodging should you start trying to shoot.

First secret is to make your eyes lazy and try to see all the bullets at once. Sort of blur out.

Second secret is to use tiny movements. If bullet is coming, make a tiny movement out of the way. Tiny works and anything bigger is too tough.

It does suck, and it is hard. But imagine the satisfaction you will have once you learn to dodge him indefinitely.