He scored 60 g+a in 71 matches as a RW for Dortmund. Yes, he played better as a LW and preferred that position, but to suggest he can't play RW and that excuses his poor performances here is ridiculous. It's clear his problem is more mental rather than ability, he hasn't taken to the extra pressure here (similar to how he never impressed with England during his Dortmund days) and has sulked rather than try and work hard. There are ofcourse additional aspects such as how he mostly played with a very attacking RB (Hakimi, Pizseck, Morey) when he was playing as a RW and transitioning to play with the more AWB was difficult, but then again he's played with Dalot, who is very attacking himself, and hasn't looked good at all. That still is no excuse for how poor he's been.
Where he is right now, I'm sure he won't play well for Dortmund as well even if they play him as a LW on loan.