4 is perfect for a D&D party. One fighter class, one healer/buffer, one offensive caster and one utility character. And with multiclassing you can mix and match to really make the 4 suit your playstyle. In this case more does not equal better.
I mean, you just repeated the same exact argument that people used to point why fours ISN'T perfect at all (in a videogame. Pen & Paper is another story): because once you have just four slots you are basically asked to either miss out a lot or to stick with these very standard roles, with "no room for maneuver"
