Ok, in your personal opinion, how much content should you be able to experience on your first playthrough?
Let me word it in this way: NO game should EVER deliberately withold content from the player exclusively with the goal of "encouraging multiple playthroughs". Which is a bullshit goal, anyway. I will play the game multiple times over the years if I enjoy the moment-to-moment experience, not if I'm forced "to go at it three times to see all the companions". Hell, chances are even at subsequent playthrough I may decide to exclude mostly the same companions for similar reasons.
I played BG2 from start to finish something like 7-8 times over the years and there were character I simply never cared enough to bring along, as there were some other that it pained me to leave out no matter having a larger party or having already played with them.