In a PnP campaign say with 4 players, I doubt any of them specifically take a 'main character' designation.
Also 'main character' is simply a different term for protaginist, in a video game its just the character you make. So say you were to play a multiplayer game with 4 custom Tav's, who exactly is the main character then?
You have a party of characters, you can choose who to use for interactions, thats how I'm certain DnD is intended to be.
But never mind then, it isn't surprising why Paladin, Warlock and Sorcerer are the most played classes, if Larian want to change that then they know what to do - make any party member's CHA skills applicable in conversation.
