Ausar wouldn't get any back cuts on Harden if Harden doesn't come above the FT line. If he runs baseline Harden just stands on the block and takes it away, he doesn't even have to move.
I would argue Mobley fading towards Cade and with one eye on him is more susceptible to a back cut than Harden just looking at Thompson.
The second paragraph doesn't really matter. If Harden is on the court any player he guards can set a screen for Cade. The fact they didn't have Harris set ball screens all night might be a good question for JB.