Even with the simplified control scheme? From HG101:
The only other fault besides the slowdown (which can be disabled via a secret menu, added to the US localization), and again this too is optional, is the default controller settings. Immediately set your controls to Novice. This will take care of auto-levelling your plane and will offer a much more natural style of arcade-like control. Although the Expert setting claims to offer a greater degree of control, with things like buttons for left and right yaw, all it actually does is distract you from the task of score-chaining, and has little to no benefit. By all means try it if you’re curious, but sticking with Novice will make finding and targeting enemies much easier, in addition to controlling your plane with utmost precision. SkyGunner is best enjoyed as an arcade-style 3D shooter, not a realistic flight-sim.
Also…disabling slowdown via a secret menu??? My curiosity about this game continues to grow.
EDIT: Oh I see it’s a mechanic, not a performance issue lol