u/John__Silver

Answer is: Switch to Novice controls. The boss fight becomes much, much easier. I think it's how they meant you to play it.

One thing I've noticed while playing AC3D is that that game's tutorial doesn't even have a proper one for the expert controls. And that ACJA and AC3D feel very similar as you play them.

Ace Combat X, JA and 3D are all developed by Access Games. And while X is more in line with Ace Combat 5 whose engine and assets it uses, JA and 3D were remade for a more "fast arcade" feel, not the more traditional "Expert" flight controls.

Both of those games are actually developed to be played with Novice Controls. Including final bosses.

When playing in Novice Control mode, Sulejmani's Action Maneuvers are less annoying and often don't make you overshoot him, while the more levelled flight allows accurately shooting him while he doing the fancy moves.

He's not an easy boss still, but nowhere nears as hard to hit as when you fly on Expert.

Verdict: the game was meant to played using Novice controls rather than Expert ones. No idea what prompted that decision but it is what it is.