Why do you assume that there will be a companion for every class? This is not a bioware game,it is larian one,and they have always given you companions in the first chapter. I don't think that they will be actual companions,maybe factions liaisons like in dragon age origins,or something similar. Most likely that is the reason why they decided to have only 4 member party. Dos2 had 5-6 companions,depending if you are custom character or premade,they also killed of the other 2-3 characters in the second chapter.
Maybe not a companion for every class, but do you honestly think that we are not getting AT LEAST a dwarf, a drow, a tiefling, an elf, and a gnome as companions?
Did you play the last two larian games? What makes you think that those are not all the companions? The loading screen shows only them,i doubt that there will be more.
According to Swen, around 130 people worked on D:OS 2, while more than 300 worked on BG3. And a D&D game like this can't have only 5 companions. It's just not possible, my mind isn't able to comprehend it. Maybe they will go for some sort of sidekicks that don't have an origin story attached and that can't be selected during character creations, but I refuse to believe that they don't plan to add new companions to the game.
Even if 2022 comes and the full game gets released without additional companions, I will still stand behind my statement.
When 2025 comes and BG4 gets released in early access, I will still stand behind my statement.
The day I die, I will die screaming that it is not possible for a D&D game like this to have only 5 companions.