Olgha
pugchamp is a medium between trying to win and having fun, if you sweat and bug it out for 30 minutes that's not really good for most pugs and most admins would agree with that i think
as a cameraman i prefer to watch games where you can follow the action, everything happens for a reason with some weird stuff happening every so often to spice it up. if you have a perma pyro who can bust his way through any flank because the other team don't know how to counter him, sure, that's their fault and it's a narrative that can be told
but most players would agree that because of scouts, pyro doesn't work at a high level very well (and offclassing a whole div below your level and going your main when you're losing doesn't demonstrate otherwise to me) and so playing it at a lower level is essentially a waste of time (assuming you want to try reach prem at some point ofc) since you're gonna have to completely change your gameplay at some higher level. this happens in loads of other games - something that's OP at a lower level (bastion, P90 rushing, techies?) is laughed at and either nerfed or ignored by players
going back to pugchamp, you're trying to emulate higher level play (which lobbies don't do effectively imo) there in a quick hop-in setting. excessive offclassing, while it may work, it isn't fun nor a learning experience for the other 11 players in the pug and doesnt simulate higher level play and so it's banned
as for 6s in general (this is just my personal opinion on enforcing the current 6s meta as has happened in the past) but heavy/sniper should be limited with class limits/whitelists because they actively slow the game down. pyro not so much, but it's a question of how crazy and dumb it is at lower divs with most of the unlocks unbanned. engi is bad except for dumb surprise factor moments and boring to play as, spy is bad except for dumb surprise factor moments and is boring to play against so those are both fine to keep as specialists imo.
final line:
GazIf its unorthodox and it works, it is aids to play against.
it works BECAUSE it's unorthodox