Idk, usually two is enough for both classes, more and you just flood the spots.
Skial
Blade D_Hero
Meowcenary
People seem to not care when we have literally 5 heavies but flip their shit when there is more than 2 snipers
Blade D_Hero
I think 2 of every class is pretty decent. But you need four engineers to be good.
DanHack
it's hard to be good as a spy and sniper and advance, but not as hard with a lot of soldiers heavies and pyros. Too many dps isn't usually frowned upon but 5 snipers who make every 4th shot isn't good. Too many supports are bad.
SgtGiraffe
it creates cancer and no one wants cancer
Kyle
Having too many supports in general is bad. Spies and snipers aren't the only ones, too many medics can screw over a team too.