Halo: CE was designed around LAN play… none of the aim assisting/bullet magnetism/auto-aim were required, except in VERY VERY small amounts. No online lag = no use for them.
Halo 2 was laughable at best. I remember the days of SMG starts on Blood Gulch while I got 30+ Sniper Rifle kills with over 25 headshots easily. I would literally get dozens of Friend Requests from that alone! Not to mention the numerous videos about it… Very bad. But the internet/netcoding were still in their infant stages, so it was required to make the game run well enough even on the worst connections.
Halo 3 was a lot better, but still was flawed. Still plenty of assistance in shooting.
Halo: Reach once again improves on the bullet magnetism for most guns, besides the Assault Rifle. That still has a decent amount. Just watch this video… Start paying attention after 8 seconds, or when he breaks his opponent’s shields. He shoots six shots total, with at least 3 with a red reticle somewhat aimed at his opponent’s head. They all like they should magnetize for the kill, but none do. Look at the last shot that an MLG pro misses specifically. His reticle was red but since he aimed slightly to the left of his opponent’s head, it went exactly where he shot. The auto-aim and aim assisting are basically the same from Halo 3 though, but the bullet magnetism on precision weapons have been minimalized.
If only it was possible to design games with minimal amounts of these gameplay mechanics… But the horrible internet speeds of America along the the netcoding just now reaching optimal efficiency just makes it very difficult to ignore the need for these features. The host advantage would be at Gears of War 1 levels… which was horrible.