Atari version of Duke Nukem 3D

[Forcie]

I never understood the functionality and means of the aiming up and down in the amiga ports of doom or duke3d. The original game wasn't using it, so you cant add a new functionality. It only serves, as you says, for slowing the engine down.

Then you haven't played Duke3D seriously ever. Major strategical game elements all depend on the mouse aiming, especially in multiplayer. I was a top player back then .
Mouse aiming or aiming up and down with keys allows you to fire strategical RPG or Devastator shots at windows or doors you suspect an enemy will turn up in as well as into flats and hiding places your enemy is hiding in, chucking pipebombs into small windows high up, placing laser tripmines at various heights on walls, not to mention orientating yourself in levels with huge height differences.

[Forcie]

Duke 3D running 68060 Atari Falcon. He also shot down enemy higher than him, without aiming up

You do not seem to understand the very simple game mechanics I kindly explained to you.
YES, the hitscan autoaims for you on the Y axis - this is NOT a reason for not being able to look up or down in Duke3D! The autoaim only works for targets you SEE.
If you know your enemy went into an apartment way above your head, and you cannot see him, but still need to throw in a pipebomb or fire in an RPG through the window to blow him up - how do you do this without aiming up or down?
This is extremely obvious in multiplayer - maybe not so much with slow and stupid single player enemies on standard maps on a low difficulty setting.