deetr, you make a good point about reducing the skill ceiling and compromising integrity of the competition for more players. The reason we all love competitive TF2 is because the competition relies on how well you can execute fights, play off your advantages and shore up your defenses. It is more similar to CS:GO than any other game in that regard, the meta revolves around a level of mechanical skill and decision-making, rather than running unlocks to counter other unlocks or running wacky team compositions. Nobody is currently enjoying competitive TF2 because of unlock cheese strats, or triple spy to mid strats, and even the occasional interesting unlock / offclass usage is more of the icing on top than what makes 6v6 such an amazing game for those of us here.
However your argument is falling down when you make these sweeping claims that all of the weapons we currently have banned are shit and would ruin the game as you know it. I highly doubt you've done the testing required to see whether gunslinger post-nerf would actually create this change where you'd want to quit the game. It's not half as bad as you think, but your instant attitude is to reject the weapons rather than keep an open mind.
We have, as clockwork said, a great opportunity to take 6s and compromise the game we've created in order to make it much larger. Let's not kid ourselves, 6s wasn't going anywhere before matchmaking. We were stagnating in terms of size, popularity, sponsorship and interest, despite being a game that lots of people here loved to play and which has great merits.
MM has provided the game a new breath of life, but the cost will be compromising the game we've lovingly created for one which will appeal to more people. In my opinion it's about having a good idea of what we think is crucial to competitive TF2 and should not be altered, and what we can afford to change and see how it works out. Whitelists (given that Valve will be working to balance them) are what I'm most prepared to change quite frankly.