Armor Lock isn't overpowered. You just suck at Reach :)
Reach isn't bad, you're just a BK :)
For my gamertag, look up "Ghoulishtie"
First off, no, there will be no flood. The flood probably didnt even know of Earths existance until that one carrier followed Truths fleet to Earth from High Charity around the beginning of Halo 3. (which at this time, New Mombassa is WAY gone, seeing as the forerunner structure underneath it, is fully uncovered)
Next, MC only met the Arbiter once in Halo 2. It was when they were both being held by the Gravemind.
The Arbiter (later sided by the elite shipmaster) made the truce with Sgt. Johnson. (when Sgt. Johnson used the scarab to blow a hole in the reinforced forerunner door of the control room for Delta Halo) It was probably during the trip back to earth from Delta Halo that they talked things over.
It wasnt until the beginning of Halo 3 that MC learned of the truce.
The thing with the hunters, was only a small group of them (including a group of grunts) assisted the elites back on Halo 2. The majority still set their life to the Covenant, and would not side with the elites. Of course we will fight everything BUT elites in ODST.
[Edited on 07.11.2009 2:06 AM PDT]