Compare to BG I or II (or indeed, most rpgs). You pick up companions as you journey along, either in sidequests or as part of the main quest.
That's not entirely true though. In BG2 you can get almost all companions after linear intriduction bit, except for Imoen for whom you have to progress through the story. In BG1 more companions are gated behind chapters, but that's not terribly good - you want players to be able to compose party to their liking, especially on subsequent playthroughs.
Of course, BG1&2 have rather different structure then BG3. While in games like BG2 or Deadfire you CAN get any (or almost any) companions you want from the get go, they will be introduced more gradually on your first playthrough. Personally, I think companions in BG3 stick out less, because how early they are introduced, but becaues like PC the are not part of the world you are exploring. I think Laez and Shadowh work fine, as they are introduced in the intro as well. But continually running into tadpoled characters who also survived, scattered across the map feels off.