Porter Jr. also loves James Harden so it is quite possible he is better on step backs because he'st tried to play like him.I don't think it is as clear as you say. He just turned 19 and he has some tools 19 year old normally don't have. I think his biggest issue is decision making and shot selection. Those are easier to fix than some other things.
His True shooting percentage was .559 in college while his ft% was 52%. That must be pretty rare. By your own logic, if he improves his ft% to just average and cuts out the long 2's he will be an pretty efficient scorer. He took more 3's than free throw attempts, so I have to figure he can improve there.