You can potentially substitute with stuff like Paladin for Warrior, Bard and Druid for Cleric and Wizard depending on how exactly they implement some abilities or certain spells. Bard can take some key wizard spells and there's spells like Healing Spirit. That said yes War+Rog+Wiz+Cle is pretty much the default.
I guess going for 4 makes the interactions between Characters easier makes game more close and personal and encounters more noob friendly. That said even though I am not in the BG3 is DOS3 faction an option to go for 6 party would be amazing and feel more strategic and give you nicer options to use all those classes and origins.
