When you create an RPG game (being tabletop or a videogame) with several options to customize your character, it´s understandable or even normal that some builds, weapon choices or party formations are more effective than others, some against some type of enemies or the setting of the campaign, others as overall all-rounders.
But a little balancing is always good because BG3 would be also a Role-playing game, so you may want to be able to play any class-race-background combination you want to play.
I mean, If I want to play a Half-orc artificer wielding a whip in the purest Indiana Jones-style I know it´s not going to be an optimum build but I least expect it to be playable. That´s even more important in MP games because you could be "forced" to play certain builds and discard others that you find fun.
I remember in NWN high-level servers you can find almost only multi-classed weapon masters of several kinds in the melee department because they are so over any other build that playing other thing is stalling your party members in high-level parties (and I am not even talking PVP here, because engaging a weapon master with another build is suicidal at best) and you seldom see a bard or a ranger of high level. I would like to be able to play without having to roll a fighter mage dual-wielding katanas or a cleric-ranger with flails or hammers because most of the weapons are subpar in comparison (and I do not want to be forced to play in story mode because I want to roll a particular character I want to roleplay that is not a power-play choice).
I agree with you, this is the reason why balance matters.
It makes no sense to have 100 classes and races in a game when 90 of them feel totally weak compared to the other 10 and everybody either uses one of the OP characters or you have the feeling that your char sucks completely.
Prof. Dr. Dr. Mad S. Tist 
