For all of its failures, the RTwP combat in Pillars of Eternity 2 was incredible. The 5 person party allowed for deep customization while still requiring you to be strategic with whom you chose to take on certain missions. Melee felt useful, ranged wasn't a crutch, magic was fun and interactive. It was the rest of the game that sucked, which is a pity - and also makes Josh Sawyer's comments about RTwP in his post-mortem surprising; by and large, the combat is regarded as the best part of the game by pretty much everyone who is a fan of the franchise.
I would like up to a 5 man party in BG3, which also allows you to add a "quest companion" as a 6th so that you can take someone along who has a quest for you but isn't on your way or part of the main narrative. That way you don't have to juggle party members mid stride and can go off on side adventures with new people all the time while still growing your core party.
I also like the BG style of having a plethora of potential companions all over the world with different stories and different agendas that you get to pick and choose from. Choosing to leave someone behind is a big incentive for replayability.