The biggest issue with the matchmaking is the number of players. Most maps in Halo 1 and 2 were designed for either 4v4 or 8v8. Social slayer can be 5v5, but the general matchmaking should be 4v4. Adding an extra player completely throws off the balance of the game.
Max Party Size 4 + Team Size 5 = 1 random child with a K/D spread of -17. 343i, I implore you to fix this issue and change the matchmaking for Halo 2 classic, team slayer, team Halo 2: Anniversary to 8 players, as well as changing big team battle to 16. 6 players is not a "big team."