This is an interesting turn in the thread! I always thought the single-player party concept in CRPG's was created just because the artificial intelligence (AI) was just not good enough.
The books suggest only a single character per player, at least in the beginning:
From the old AD&D PHB, "The Dungeon Master is advised to limit player characters to one per participant at commencement of the campaign, though as play progresses, additional player characters may be added in a judicious manner."
The 5E Player's Handbook uses singular language, "Your first step in playing an adventure in the Dungeons & Dragons game is to imagine and create a character of your own ... Once completed, your character serves as your representative in the game, your avatar in the Dungeons & Dragons world."
This is how it has always been for me. I have never played a D&D game, TT or video game, without playing a character I created. Having said this, when it comes to my companions in a party-based video game, I only play with the provided NPCs and never ever custom-created "mercs" (unless there is no choice like in the IwD games).
