Talk about shoehorning. Varion is king, just because? Or, how about, he's king because his father was king? King Llane ring a bell? And that he was an original member of the Alliance, under Lothar? And that he was the King of the biggest human kingdom left standing after the wars?
Varion's story is well documented, and is not "because varion". He fought for his throne, and fought to keep it, and earned his leadership of the Alliance through being a masterful military leader.
It's not a title a young king should get, as a consolation prize because his daddy got ganked by some demons. It should be earned. Varion earned it, and they wrote the lore to support it. Anduin hasn't, and they're going to have to recon the living shit out of his story to make him a plausible general and leader.