I don't think Team Battle mode is really comparable to WMM or CotS in terms of content.
WMM requires that they design lots of special match conditions, design lots of alternate weapons, balance them all for difficulty, and create a menu interface that makes sense for that. CotS requires them to design a bunch of maps, generic enemies, a level-up system and balance it all for difficulty.
Team Battle is just versus, but the character changes at the end of the round. Admittedly, it does get way trickier if it's online. But the point remains: significantly less content is required to implement this mode.