PAPASTAINthe demoman is so balanced that you have a single spot in 6s entirely dedicated to him, when even roaming players sometimes get to switch
people still think this?
Demoman is limited to 1 because it's obvious it's a very specific and defensive class within the metagame. The game has been played competitively with 2 demos before and it was too stalematey, that's why it was changed, because the demo being a mostly defensive class would stale the game a lot if there were 2 on each teams.
Same way there is only 1 medic allowed, with 2 medics, both on uber the pace of the game would be a lot more slow and uninteresting. It has nothing to do with the class being over/underpowered.
Demoman (stock weapons) is a perfectly balanced class. It's hard enough as a demo being the one supposed to damage deal while being targeted at all times, if you nerf any of the stock demo weapons that would have a substancial impact in the metagame, not to talk about how useless the class already feels in close combat... There's nothing worst than going head to head with a scout while you are alone. that is a scary thing, because you know even if you aim everything perfectly the bastard will still dodge it, and because you have no hitscan weapons you have no reliable weapon to defend yourself without taking damage unless you use the melee.