the thing with your argument Arx is that those games have public modes which were specifically designed by the game developers to be competitive and they were the ones that set the standard in terms of competition format
TF2 never got anything like that, so the current 6v6 game we have is basically the result of players of the game experimenting for years with different restrictions/maps/game modes until the one that was the most competitive and enjoyable was reached
if valve had come out shortly after TF2's release with this arena respawn format I think 6v6 as we know it probably wouldn't exist
i think this format sans the class bans (which I think are pretty arbitrary and would just mean that some classes never see any play time) is probably the best case scenario for any matchmaking system (if they do end up releasing one) as i cant envisage 6v6 ever getting valve support, ever