Mapleyou just get to a point where a scout will be the best option the majority of the time.
hence the one player limit on each class, meaning 2 scouts would be disallowed. you are right about the cycle not actually cycling, but worse than the 5th always being scout and therefore essentially going back to 6s, the 5th would in most cases be either a sniper or a heavy, depending on context. and no one wants to play against full time sniper, much less heavy (especially in matchmaking where successfully focusing a heavy would be near impossible). heavy/sniper would probably be so viable that i could easily see the scout offclassing to the other as well, and engineer/pyro on lasts.