The difference is that Mads Pedersen is very fast and often has the role of a leadout man whereas Fuglsang is sort of a slug.Sort of
On a serious not I don't see why he can't out sprint Nibali for example, or Bernal, or even tired Valverde. Stranger things happened, we saw last Sunday something similar.
I also think that he would have a fair chance of beating Nibali or even Bernal, should it come to that, but certainly not Valverde even if his sprint seems to have deteriorated a bit over the last year.
How Fuglsang managed to beat Alaphilippe in Amstel is still a mystery to me and I have to see something similar happen again for me to actually believe that he can do stuff like that.