WoD was destroyed thanks to MoP feedback where everything outside of raids should be optional.
So keep that in mind as you once again complain about things being "mandatory for raiding".
Whenever I see people complaining there's too much to do in Legion I know that Blizzard is on the right path again.
The sha are byproducts of the Old Gods and Emperor Shao Hao's emotions, but don't seem to necessarily obey or work for them, they just do whatever they want. The Sha seem to be to the Old Gods what the Saurok are to the Mogu.
Hence, since they're not actually aligned with the old gods (and as a result are hurting the mantid by pushing them too hard), the Mantid oppose them.