Despite being an MMO, solo content has always had a place in WoW. Let it be goldfarming, running old content, farming collectibles, doing the Mage Tower, there is certainly a demand for it. These activities are generally separate from pure endgame activities. However, these solo activities have been turned into a way to progress in group endgame content (PvP, M+ and Raiding).
With the advent of Titanforge, Warforge, Corruption, RNG legendary drops Artifact Power grinds and Worldquests, solo content has turned into a pretty much “must do or you’ll miss out on crucial progression” content, essentially inspiring FOMO by making you log in every day to do that ONE World Quest that just MIGHT give you a 445 crit-haste ring with TD3, Leech and Avoidance on it, so that you can also Socket it later on.
On top of this, solo content such as Visions of N’zoth, Island Expeditions and Torghast that would have been fantastic stand-alone solo content, filled with its own separate progression system and expanded lore have instead been twisted into ways to further enforce solo content into the main progression loop in a way that was unfun and unproductive (here’s where the obligatory Old content must be kept relevant - #7 - WoW Community Council - World of Warcraft Forums (blizzard.com) link comes in).
Imagine how fun would it be if Torghast was just it’s own piece of content instead of being a conduit for legendaries that are going to be gone by the time 10.0 rolls around. Imagine having a mode similar to Palace of the Dead in FFXIV for Torghast. And that’s true for Islands and Visions as well. Instead of being something that you are pretty much obligated to do, it should be something that you can do if you want during downtime, something that can be the 4th pillar of endgame content in WoW - next to PvP, M+ and Raiding.