I was never any good at aiming with the analogue stick in FPS games. On the deck I'll usually use the trackpads (configured as a trackball with haptic feedback) to aim approximately and then gyro for fine tuning, and I've found my aim is significantly improved. It's no keyboard+mouse, but it's close enough for me, that unlike with the analogue sticks, I don't find myself needing to reduce difficulty levels or enable any kind of aim-assist.

I sometimes find myself wishing I had a controller with the same layout as the deck that I could use when I have it docked to my TV.

I've seen people use a combination of both. The analog stick / trackpad for macro movements, and the gyro for fine tuning. I tried it once, and I think it could be fine if I practiced a tiny bit.

But I've also got a normal PC with keyboard and mouse, so I don't need to.

You can also use the touch pad for aiming. Or turn on gyro only when touch pad is being touched, which is useful for micro adjustments. Pretty customizable, although I mostly just use the sticks.

I played Prey and Tiny Tina's on the Deck, both of which worked pretty well

Either work just fine, IMO. The gyro is just as good as on the Switch

They've added in aim assist for the HL rerelease, at least. Annoyingly it's on by default, even in the PC version.