I think I speak for a great deal of many, many players – When I say we enjoy class questlines.
- Sure, I understand it’s not for everyone, fair enough – but many? Absolutely.
For example, in ‘Legion’ - albeit not ALL classes, however with a great many I quite enjoyed the class specific questlines 
They felt intuitive and made your class feel ACTUALLY significant to your character and made your power-level of said-class feel actually recognised.
Whether it’s:
- Being a virtuous paladin, saving those in need from bloodthirsty, hungry undead that gain power from the more of the living they devour.
- Mages who are banding together with the blue dragons & netherdrakes to tap into tremendous power to give them an endless font of magic outside of Azeroth alone.
- or being a demon hunter blacking out and getting a questline where you’re awaking in a cage and told you’re going through the chaos hunger — The hunger demons get to feast on magic, power, the living … or other demons, yet come out more powerful by the end of their feast → Being redirected, along with some other demon hunters - To put such hunger to good use, as opposed to hurting innocents and unleashed upon a demon world to slay demons — feast on them - and ascend your powers further.
- Being a Death Knight who’s on behalf of the Ebon Blade is to investigate the undead numbers rising TREMENDOUSLY – To find, hunt and exterminate the Dreadlords who are bringing about a new plague of undeath spreading across Azeroth.
- Priests on the frontlines of mending the sick of those struggling with the plague — unable to tell which is simply a simple plague of fatal proportions – or that which is such with the addition of undeath attached to it.
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- Later on making a bargain with the Forsaken to attempt to reach the minds and souls of the newfound undead and unshackle them with priestly magics (or find those that did so of their own pillpower) and find them a place in the world.
- and assisting the Paladins who are being pushed back, on the precipice of defeat due to the overwhelming strength and numbers of the undead hordes – Requiring the priests to save the Paladins for once …
- Druids finding the conspiracy kept by the First Ones that souls in the Shadowlands don’t ever truly die – They are refined to an indestructible spark, hidden within the stygia of their collapsed form. Druids then seek-out various Loa and Wild God soul-sparks to pry them from forces who’ve also discovered this, and claim them to restore once more.
- Monks also discovering such a conspiracy, finding out the soul-sparks of mortals drift to an ethereal plane that’s locked away — Going through a grand adventure to find out how to tap into the eternal power, of the element of spirit – So they can traverse the planes to this realm, and then weave them into a flux created by monks all over Azeroth — To reincarnate into the cosmos.
And so on … Such questlines that provide an array of rewards for their class.
The above are just narrative-examples I came up with, they don’t necessarily have to be THAT haha, but you get the idea. 
Anyway, there you have it guys!
I hope most of you have enjoyed the thread, if you have any great suggestions to add, or any intriguing thoughts to share – Feel free to comment bellow! 