i feel like the biggest hurdle we need to overcome for this "discussion" is that the reality is 6s might as well be a different video game from tf2. it takes everything good about tf2 (movement, high risk/high reward guns) and leaves everything that is not necessary for a competitive environment (huge team sizes, maps not conducive to coordinated play, silly/overpowered weapons)
the identity of 6s vs the identity of tf2 to people who have either not played 6s or not played tf2 in general are so vastly different that trying to get a pubber into 6s is like trying to get someone into TF2 for the first time. either they like what's on offer by 6s or they are completely content with their silly mode (which there's nothing wrong with enjoying, i like to pub from time to time too)
its also hard to convince a pubber to want to play if they main an offclass, especially stuff like pyro or engie that have practically no transferable skills to the 6s classes. why would i learn a whole new class i don't even like to play competitive?
i had to explain to a group of friends that in 6s, the classes are hardly even classes anymore. they're more like weapons in the buy menu in CS. you just can't get away in CS with running a P90 every game at the high level, but at the low level you might, and even at the high level the P90 might have some uses on some particular rounds, but not enough to main all your time into practicing it