Wow! Congratulations, the boss is supposed to be almost impossible to defeat. The reason he is so unbalanced is actually because I haven't developed anything for after the final boss.
That being said, you have raised some excellent points.
Firstly: attack patterns. Right now enemies might seem like they are firing all of their weapons simultaneously and it just gets chaotic. I could implement attack patterns so that similar weapon types fire around the same time, thus creating an "attack" that the player must learn to counter or avoid.
Secondly: specialty bosses. I am currently working on a series of updates that can greatly help with this so that enemies can take on a more niche role to test the players skill and ability.
Lastly: a ramming final boss. I have some plans to make the final boss more interesting and challenging without just stacking his health and damage. I'm thinking of a multi-staged boss whose behaviour changes as he loses health or even a few powerful but smaller bosses to fight simultaneously. If the player did have to fight multiple enemies then I could have three different classes (trireme-ramming, interceptor-fast, dreadnought-tank/damage).
Thank you so much for your feedback! I'm very glad you enjoyed the game.