Eliminate death match from the mix entirely.
Add 1-2 points per kb to all game modes.
Now you can kill your way to victory (slower) or do the objectives, or both. The objectives being a counter to deathmatch style teams, so that weaker teams have a shot at placing.
If the dm setup team is worth their salt, they'll stop the others from completing objectives. If the objective setup team is worth their salt, they'll have counters for the dm teams.
Shift or modify the deathmatch achievements to general "battlegrounds achievements".