As soon as I discovered in 1999 that you could create an entire party from scratch if you start the game as multiplayer game, and then just move th save file to single player, for 20 years I asked BG1 players to try to convince me, what's the point of Jaheira, Imoen, Minsk or all these loser characters when I can roll myself 6 near-perfect stats characters with no flaws, all the skills I carefully picked for them, and best of all, they keep their mouths shut and never bicker among themselves!

Sure you could make a case for BG2 because of the vastly improved dialogue and character specific quests, but in BG1 that's just not there.

Imoen, Jaheira and Khalid aren't pointless at least. They are tied to the story.

You are more than welcome to create a party of 6 PCs if you like, of course. That's part of the fun of playing the IE games. :) (Indeed, the Icewind Dale series caters specifically to players who enjoy that playstyle.) For me though, aside from the roleplaying perspective of bringing along 5 other companions with their own personalities and agendas, I also find it fun to create builds and equipment for them that shore up their weaknesses, of achieving victory DESPITE their shortcomings. Gorion's Ward may be godlike in comparison to your allies (as befitting your heritage), but I find it more engaging that your character would not have been able to achieve victory without the assistance and support of their flawed mortal companions, that there is value and purpose to be found even if you come from humble origins.

I would assume the whole point is adding some realism, and some level of immersion. You're naive and just had your foster father murdered in front of you. You are desperate. You'll take whatever help you can get, regardless of their "power" or nature (like evil Monty and Xzar). Gibberlings can kill you right now (at Level 1). You're a beggar, not a chooser. In real life your traveling companions have voices, thoughts, and opinions, and they may not get along all the time. That can be a hard lesson to learn, just like when you finally meet Jaheira and Khalid, and if you kept Monty and Xzar along, the inevitable fight happens.