I generally think it's a waste of time to compare players across eras, and nowhere is that more true than at point guard.
How do you compare Cousy, with the rules and strategies of his time, to Robertson... to Magic... to Stockton... to Nash... to Curry? The rules have changed, the strategies have changed, the workouts have changed, the skillsets have changed. There wasn't even a three-point line when Cousy and Oscar played, and it wasn't such a dominant part of NBA offense until recently. Even Nash, who is more recent than the other players I listed, played in a much different NBA. If Nash's peak coincided with today's NBA, then he's a guy who is probably jacking up 8-10 threes per game at 43% and his inability to defend matters less because nobody can defend point guards with today's rules anyway. But we don't know that for sure, because you can't accurately translate a guy into another type of basketball and then compare them.
All of those guys are the best of their era. Curry is too. I think diving any deeper than that is impossible and therefore pointless.