Harden On/Off:
On: Rockets +8.1
Off: Rockets +6.5
LeBron On/Off:
On: Cavs +9.4
Off: Cavs -7.3
LeBron is not losing leads, the rest of the team is when LeBron is not on the court. Something that Harden doesn't have to deal with because the Rockets outscore opponents whether he is on the court or off.
Harden also only plays hard on one end of the floor, and has a negative impact on defense, a big reason why the Rockets don't have much of a drop off when he leaves the court.
bingo