As explained so many times on the forum, human animations are limited by the limited number of skeletal bones in FSX compared to P3D4 ( 22 vs 64 ), so they look less natural.
The next major update, in addition to PBR, will introduce a lot of P3D4-only new animations which looks way better. We can only hope more and more people will just trash FSX, so we can move forward with better products.