Postums has posted a playlist update for MCC based off of feedback given this past December. Changes are as follows:

Social Matchmaking – 4v4

Halo 3 Slayer – Lowered weighting of AR start entries which are now 50/50 split with BR starts

Halo 3 Assault – Added in Multi-Bomb Assault for Assembly, Citadel, and The Pit

Social Matchmaking – 8v8

Halo 3 – Added Sandbox variant Entrenched for BTB Slayer, Multi Flag, and Neutral Bomb

Halo 3 – Total Sandbox weighting pool is the same, but each is lowered with addition of Entrenched

Halo CE – Ice Fields CTF has had its weighting reduced due to highest quit rates

Social Matchmaking – Infection

Halo 3 – Hide and Seek has been removed based on overwhelming feedback.

Halo 3- Weightings in this playlist now better align with legacy Living Dead playlist from Halo 3 X360

Competitive Games – Halo 3 Lone Wolves

Lowered Objective game type weighting

Slayer / Objective is now an 80%/20% split for weighting

You can view the original post from Waypoint here.