We do not talk enough about this. It is good to have a threat specifically made to talk about party mechanics and interaction. It was a central point in former bg and IE games. Also in several Larian games.
I´ve had my blast with W2 and the NWN 2 Storm of Zehir campaign. Create a party of 4 and recruit new companions with their own personality, agenda, etc. I liked the middle ground between party creation and companion banters.
But I have to say that the thing I liked the most about Bg games (Also NWN2, DA, P:K, etc) was the companions and the relations with <charname> and the other companions of the party.
I understand If they let you hire and create your own mercenaries ( Games like P:K or DoS2 allow you do that) but I prefer an entire party of sentient, talking companions you can interact to and listen while they talk between them.
One thing I liked about DoS2 is the fact that you can choose your companions´ base class in a dialog before recruiting them. In some d&d NWN2´s mods, you also have this option. It is one of the few mechanics of DoS that you can safely implement in a D&D 5e simulator (And I think most of us agree that is what we want, a D&D based game). That will also let you mix parties that you normally do not take, because they have duplicate roles, etc. You only have to choose the characters and party you like most, all for RP purposes, not utility purposes.
I could be challenging because you do have to create a companions´s background that can adjust to different classes, but It would be worthwhile.
If we say Baldur´s gate: a classic 6-men party. If you have the huge number of roles, skills and classes of 5e (even if they do not let you choose all) I think is a fair number. Also, the more companions, the merrier. In DoS2 they made a mod to be able to have 6 companions anyway, and that mod had like 2KK downloads, so they better do that in the base game so we do not waste time
-Can the PC (if I'm wrong and there is a single protagonist) be one of the Companions like on Divinity: Original Sin 2?
It would be awesome. Adds replayability and also allows you to live the adventure in different perspectives. To be able to finish a campaign and later can restart and shape the story of one that was one of your former companions (and usually learn more about them, his/her story and motivations) was refreshing and one of the things I liked the most. That also allows you to have different origins, not the same I-am-a-baalspawn- from-candlekeep (for example) for all characters.
I like that type of details. In DAO the different origins mechanic was masterfully made, but I found in DoS2 the part about the companion-that-can-be-a-MC refreshing. Makes you feel part of a bigger world, not the center of a world specifically made for you.
But in a CRPG game, I expect that you also have the option to create your own character, background, etc and RP according to. Because most of the time that is what you want when creating a character in this type of games. I do not think that would be in question because the game has MP and the devs of larian already took note of it in the kickstarter campaign ( originally in DOS you do not have mercenaries or in DoS2 you were not able to create an original character. The companion origins are still far better than a new character).