Larian has said it'll be 4 because it will make combat smoother and take less time. I understand that point, it's not a bad point, but I feel like it should be five, because a balanced party typically has four roles to fill: Melee fighter, Healer, Lock and Trap remover, Offensive Caster.

Original Sin was classless, and characters could mix and match roles fairly easily, but D&D's system is class-based, and there doesn't seem to be much room for party flexibility with those roles filled, and multi-classing isn't a solution, as it makes you worse at multiple roles at once.