First, I think Huangshan's a more dramatic experience than ZJJ, quite a bit more dramatic By comparison, ZJJ was something of a letdown for me.
Second, there are interesting old towns in the broad vicinity of Huangshan you can visit with your extra time.
Third, getting to ZJJ takes you quite a distance and hassle from Hangzhou. Huangshan is so much nearer.
I have been to all these destinations, and I would definitely include Huangshan. I also think Shanghai deserves more time than the OP is giving it.