Jeebs, let me know if this helps because I play against friends that play EXACTLY like this, lol. It's typically Steph or KD and it's head to head, not online so YMMV.
As other posters indicated, use protect the paint. NEVER use physical defense unless you have a perimeter oriented player and you'd like hard close outs. In the paint, your players will foul much more with that setting on.
Deny Harden and moderate on-ball because he seemed reluctant to shoot the J. Double on drive for Harden and go under screens and send your bigs under the screens as well with a soft hedge. For other perimeter threats like Ariza or Motunious (Butchered spelling), Deny ball so the double comes from the correct personnel (Mike Conley and Marc Gasol). Another IMPORTANT aspect is to pre-rotate on driving threats like D12 and Montunious.
I watched the vids and how often do you use LT when defending? Anticipate where he is going (He seemed easy as he only really wanted to go baseline) and utilize LT and the other back button to bump him and slow down Harden's moment. Once you bump him and have your defense in position, start bringing your help defender (preferably a big) between the free throw line and the wing. Ideally, your double should already be incoming pestering his additional dribble moves.
Next, anticipate the pass and this is why it was imperative you put pre-rotate to on with the bigs! The help will help the help and if done correctly, plenty of turnovers and easy transition buckets until he opens the floor and utilized Harden as a facilitator and makes the extra pass to find the open man.
Lastly, don't let him dance around you with Harden. Remember how GS exposed Harden on the close out game constantly pestering him with several defenders and never letting him get into his signature ISO moves? If I remember correctly, he had 12 turnovers. If he still got his with these adjustments, send the double on the catch and deny (or tight) appropriate personnel. LT is your friend Jeebs, press the hell out of too!
Let me know if I helped at all.
P.S: You still got jerked on a few possessions.. In my crib when we play we call that "2K Love" and also, "shout out to my _____ 2K" salutes too haha