But there are others who do damage. And potentially others who tank. So there's always someone "on the other side of the scale".
"What, you're the only one doing AoE damage? Then add a bonus to all of it - don't worry, it's still balanced."
You are all on the same team. You are all trying to accomplish goals together. This isn't WoW where people get all persnickety about "their numbers" and making it a contest on DPS or any of that crap. No one at the table with any sense should care if one PC is doing 10 damage a round while another is doing 7 damage-- especially if that 7 damage PC has other stuff they also do instead.
So long as those disparities between the PCs aren't so great that the other players at the table feel like they are
extraneous to the one other remaining PC and didn't even need to be there... there's no reason for them to care how their other teammates are doing. All of them should want each of them to do really well! That's the whole point! What, the Wizard player is going to be mad that the Dex barbarian does 20 points of damage to a single other enemy, while their single spell attack might only do 15? Of course not! "Oh darn! You are helping us win this fight too easily!"
Especially not when that Wizard could just as easily thrown out a AoE spell and did 12 damage to four enemies at once for 48 points of damage. And why in the heck would a paladin care that the Dex barbarian is also quote/unquote "tanking" and taking attacks from enemies and absorbing damage too? You think the paladin player is going to complain about not getting hit as often and say "No way! I'M the only one allowed to get the crap kicked out me!"
Balance is relative, it's not absolute. This game is not in any way, shape or form built such that every single PC is going to be completely
equal to each other in melee damage, ranged damage, AoE damage, armor class, skill use, saving throws, spell effects, etc. etc. etc. But at the same time... none of these classes are designed such that you can reach any state of being "overpowered" with them no matter how you build your character, assuming you aren't intentionally making your PC bad.