I don’t know why the Halo Official Site has even less avatars themed as “Halo” than Microsoft Account does. I cannot have ODST or Noble or Red team as my like to choose. And most of all, the account which displayed directly in-game is my Halo Waypoint account, neither Xbox Live account nor Microsoft account, why? Free to point me out if I have something wrong. Noticed this when running MCC for PC insider Flight 3 couple of days ago.
You get more avatars unlocked on here as you rank up by posting.