In the very, very beginnings PCs were just kind of special forces. The very first "PCs" were just unique battlefield commanders and spellcasters. There was no intent other for them to be a unit of 1 individual originally.While obviously the game has it's origins in wargaming and miniatures, I don't think I'd call the role playing part incidental. After all, the whole point was to take the wargaming aspect and bring it down to an individual character level. Which is the root of role playing. So I think that part was very much part of the initial goal.
But that wasn't really D&D yet, it was a wargame with unique battlefield commanders. I'll see if I can find the interview later.