I think a dedicated heavies playlist would be really fun though I like the idea of a TU playlist too. It's actually really nice for teh days where you want to use an assult rifle because it helps the weapon to be more accurate. Also, with the TU the pistol becomes a weapon of skill that, with less bloom, can be used effectively.
I TOTALLY AGREE about the DLC comment you made. I have 77 of 79 GamerScore on this game adn I desparately want the last 2 but I have NEVER found a single online match where I can earn the acievement. I think they need another DLC Objective Playlist (like back in Halo 3) that would also include Invasion. I personally love the DLC maps and wish I could play them more. The only reason I bought them, however, was to finish my gamerscore on this game. So until that happens the Slayer DLC doesn't do much for me.