Few things to add.

1) 6s attempts to allow players to have the potential to basically move as fast as possible. 5cp is the best mode in tf2 for this. Koth is good as the point can change hands based on a series of good plays. Modes like payload, attack and defend, etc promote one team to remain stationary while the other constantly throws themselves at the other team. The potential for back and forth action is limited as one team is always constrained by the objective while the other is not.

Not all matches last close to an hour. Sniper and or spy are run to combat enemy snipers as are sacs. It’s worth mentioning that other game modes force more classes to be run by fiat and, sorry, players in these modes tend to not be as good as 6s players on average. Highlander, which requires 1 of each class to be run, is completely centralized on demo sniper and med at high levels (honestly centralized on sniper) because of player count and map design. Sniper is not fun to play against when