Main: Medic
Hours Played: 4,205
Years Playing TF2: 5

I think that what needs to be understood is that, as you said, competitive 6s will also be a cookie-cutter class, with 2 scouts, 2 soldiers, 1 demo, and 1 medic. Implementing a "less formal" version of competitive tf2 won't change that in my opinion. The reason for playing competitive is trying to win, so in order to win everyone is going to play the cookie-cutter classes. Furthermore, if someone on a 6's team goes pyro or engineer permanently for the match, they are going to get shit on by everyone else on their teams, which means that playing pyro/engineer won't be fun at all. That is why I think that both systems need to exist, so that pyro/engineer mains can play competitively but also in a friendly environment.