Priests being in power makes a lot of sense. Let’s look at the other classes:
Rogue- being a leader is counterproductive, you want to be unknown, operate from the shadows, if your job is done well no one should know you.
Warlock- Universally feared/hated, or a least mistrusted. Cannot lead.
Druid- Often more concerned with the world itself to truly be faction bias, which is what leading requires. Druid is probably the most neutral/cross faction cooperating class. You could make a similar argument for shaman, though shaman leaders on the Horde is pretty common, they function as Priests in horde societies in many ways.
Death knight- See Warlock
Demon Hunter- See Warlock
This leaves: Priest, Mage, Warrior, Hunter, and Paladin, and Shaman as falling naturally into the role of leader, with warrior being a wildcard that can be just about anything really.
Lol. Anduin is a priest. He drops his sword mid battle and heals, he is sub par in martial combat, he uses large AoE heals, goes to netherlight temple, and has been confirmed to still be a priest. Paladins converted a priest to paladin in Legion, it wasnt Anduin.
Hero lore characters have always been this way. As well, there are game mechanics created for the sake of gameplay and convenience that arent quite the same on the lore side. I res people everyday i play, but in lore its a very rare thing and requires extreme power to successfully perfrom. This is why Calia is undead instead of living, and that was two powerful priests and a Naaru. Jaina can teleport an army and raise and fly a freaking ship but regular mages can not. Thrall called forth a fist of fury to squeeze Garrosh. Malfurion literally buried hordies alive with a root spell. Tyrande uses a bow. Sylvanas… She is kind of her own banshee hunter class thing. They have base abilities, beliefs, and/or roles that define what they are; but theyre all able to go outside the confines of game mechanics.
no, she hasn’t. The cdev was deliberately stoking a fire. Naaru have some overlap with Elune, just like they have some overlap with demons in their attributes. Elune is not a naaru, it was never confirmed. Legion showed up Velen was being lead around the nose by the Naaru, who mislead as needed to keep themselves in the spotlight. We see the Naaru aren’t as benevolent as they were portrayed in BC with the Maghar story and Illidan killing Xera for her pushiness. Elune is quite different. I suggest you stop cherrypicking things and go read the entirety of her lore, including the pre-cata quests about her.