The problem with 'bridging' the casual -> competitive gap with matchmaking is that being effective as a team in tf2, at a competitive level, requires making friends with 5, 6 or 8 other people and getting a good grasp on how they tick.

Casual matchmaking forms the exact opposite habits that you need to form a team. Teams form over long periods of people getting to know each other in community servers, not 2 minute stompfests that instantly rip each player away from each other once the gaming quota is up.