There are two James Hardens. One plays with Kevin Durant and Russell Westbrook and the other plays with the likes of Nazr Mohammed, Nick Collison and Daequan Cook.
With Durant on the court, Harden averages 11.2 possessions per 36 minutes. With Durant out, he averages an extraordinary 23.1.
The second unit may place at a faster pace than the team average but if we assume the Thunder's pace of 93.5, then Harden uses 37 percent of possessions, while assisting on roughly 27 percent of teammates' baskets for the second unit.
I should note that saying "without Durant" is largely saying "without Durant or Westbrook" because Westbrook has only played 20 minutes this season without Durant.
Harden without Durant puts up numbers rivaling LeBron James'. His 37 percent usage and 27 percent assist rate compare to James' 33.0 usage rate and 36.2 assist rate. However, Harden is shooting even more efficiently than LeBron with an absurd 67 true shooting percentage, while James' current mark of 61.3 is higher than any season in his career.
For about 10 minutes a game, Harden looks like LeBron James with a bunch of players with limited offensive abilities. Playing against other second units may make points come easier to Harden, but what he is doing is still incredible.