springrollsGJ3TLDR: on principle banning HL players from playing pyro heavy engi spy is objectively stupid because these classes have very little impact on 6s gameplay in the way that the standard 4 classes do. having a “good” vs “bad” heavy/pyro/engi player has very little bearing on the success of that class being used, what actually matters is understanding the context in which these classes are powerful.
Possible I'm misunderstanding your point here, but I agree with this sentiment if people were trying to play "optimal 6's" in which case yeah putting an invite pyro main to airblast on gully last barely matters. But if you are already resigned to playing perma heavy/pyro and understand that a lot of the time they are objectively the wrong choice surely having an invite hl main on those classes is better than random combat player from x div if the div is low.
of course, i wont undersell the fact that each class in the game has a lot of potential to squeeze out, and than an invite HL pyro can make much more of the class in 6s than an IM scout offclassing to pyro can. the point i’m making (and that im sure you already understand, just reiterating for clarity) is that by nature of running pyro in non-standard scenarios being so much worse than having the standard composition, that “potential to squeeze” has far less impact on the game therefore letting the invite heavy run perma pootis isnt a big deal/not worth class restricting in the slightest.