lmao, you must be new to xbox. Halo 3 was released in 2007, I believe COD 4 was released like I don't know around 3 months later. Even after 2 years (2009) Halo 3 had well over 300,000 people playing the game, it wasn't until MW2 when that number took a huge hit to about 100,000 and then when reach came out it dwindled to about 10,000-30,000.
If halo 2 did come back and it had achievements but had same old graphics same old campaign same old button glitches, etc. etc. It would easily hit 100,000-300,000 people and it would probably stay that way for a while.
What you are saying about halo 2 on the original xbox had no competition, I don't disagree with you on that. I just believe that halo 2 is better than most games now and if you asked anybody who played it a lot they would tell you it is WAY better than reach or 3.