DSR Chainz, I'm not going to quote your whole post, but let me reply.
Brutes were used in the first battle with humans by Truth, where they had armour, choppers, spike grenades and spikers. He had plans for them to be in power for awhile. The Elites going off to protect the remaining Prophets is reasonable to me. Truth would use any excuse to get Elites out of the picture, and bring Brutes in. This fits well with the timeline and Truth's character.
Spartan lasers and mongooses were not invented a couple of months after Halo 2. Just like BRs weren't invented in Halo 2.
Everthing in ODST is within canon.
Look, nothing was wrong with what they did with the game. Elites aren't that important, anyway. I find Brutes a much more suitable evil alien.
[Edited on 06.10.2009 2:45 PM PDT]