"Imagine 5+ bowlers all using the same lane. The more bowlers you have, the more you will have balls bumping into each other, getting in the way, crossing paths, and falling into the gutter."

I suggest THAT is the problem. TDD is a band aid to cover the fact that such a team cannot function. The right team of <=4 can blow the roof off of ANY team of 5+ based upon communication network overhead alone. If you don't have the right team, you are hosed no matter what.