The failure of FACEIT (more specifically, the competitive 12v12 clan wars I played in with comms) is already an example of why competitive 12v12 with no restrictions does not work. He of all people should already know why incentivizing groups of comp players to "tryhard" on pubs leads to degenerate tactics and awful matches, because he was the biggest complainer when FACEIT 12s were a thing.
At lower skill levels it devolves into ubering the Phlog Pyro to wipe out uncoordinated players and turn a 12v12 into a 12v5 or worse. Can't imagine it would be very appealing to pub players, even. The only reason pubs are enjoyable is because most players deliberately ignore the best strats, goof around, or they're simply too bad at the video game to abuse stupid unlocks.
Edit: Oh lol someone already brought this up, I can't read