I don't know if Xu Xin's problem is so much that his backhand is bad (and I've been one who has said that several time admittedly) or more so that he puts himself out of position by running around it too much for today's game.
Look at the tactics he selected for this match. He served from the middle of the table a la Wang Hao and simply opened himself up to be able to cover those wide FH shots and was willing to play his backhand. At least for this match it worked.
If into a rally he starts to run around some balls, fine. All pros do that to some extent.
But he had moments of falling back into that old Xu Xin that either with the old spinier ball, or him being younger back then, worked back then but gets him into trouble today.
Check that point at 8:05.
I've even put it in infinite looper here for anyone interested.
http://www.infinitelooper.com/?v=giBQaZU2m-E&p=n#/485;489
That's classic old school Xu Xin that he just cannot do today. Maybe in the past that forehand he'd hit would out-spin someone but he just can't put himself in that position in today's game. Serving from the middle of the table pretty much forces his hand at playing that 3rd ball as a backhand.