ROFL. Everyone is dancing around the problem. In BG3 theres what 6 maybe 7 playable NPCs?????? Versus 15 in BG2 plus tons of modded NPCs. Theres your answer why its a 4 character party game. Frankly, Im surprised it isn't a 3 character max party.
Cherry on top is, you will NEVER get modded extra playable NPCs, unless Larian makes more. Thanks in part to cinematic dialogues.