Curry's offense is so far ahead of everything else that AD contributes that it's just not close imo, scoring in basketball is that much more important than everything else, and Steph can score from anywhere inside half-court and he's also an excellent ball-handler, passer, and a good rebounder for his position. Harden has been carrying G-Leaguers the last month or so in a way that AD has never been able to do.
Harden is having a historically great scoring season, on incredible efficiency, he's not Russell Westbrook. He takes 40 shots because he has to and scores in a way that almost no one in the league can, certainly not AD.