. . . but what position did Robertson play, literally?
He was a combo guard, and had most of the ball-handling and distributing duties. He's commonly referred to as a point guard, though. See, for instance, here: Link.
Most, if not all. He was averaging 11+ assists in a time with different rules that made assists a lot harder to get. Cousy was a full-time PG and he was getting more like 7 a game.
If Magic is a PG then Oscar is definitely a PG
If LeBron is a PG then you could argue an incredibly long list of non-PGs that could also be considered PGs, and you can pretty much make an argument about every player being considered a different position than the one they actually play. That's why terms like PF/C, combo guard, swingman, and POINT-FORWARD (LeBron) were created.
As far as actual positions on the court, there's only 1, 2, 3, 4, or 5 and LeBron is without a doubt a 3.