Man I could do a whole long post explaining this. I'll try and keep it short.

MMOs are not books. The villains exhaust much faster because you are exposed to them more frequently (repeatable raids, dungeons, dailies). Your character is also not unique (10 million players) so you have to rely entirely on villains who are played out during a raid cycle. Since you can't rely on a strong player character for immersion you need NPCs, and friendly NPCs take the spotlight from the player, so you can only rely on villains.

I think the storytelling in WoD is the best it's ever been

Wrath had some flaws but Wrath told it's story better than any other MMO I can think of. Arthas interacted directly with the players and responded to them in meaningful ways. Events occurred which changed the world around you. You built up an assault on a powerful enemy, and the stakes were appropriately high.

The Iron Horde was beat back by versions of ourselves. We shoved them in to a portal with apparent ease. Three people plus a handful of guards can hold off their assault on our main base. They do not interact with the player in the same way as Arthas - you have to go to them and fuck with them before they antagonize you.

with the recurring antagonists and heroes

Having recurring characters is pretty basic to storytelling. Yrel could be interesting but her character so far has been "girl what doesn't want to fight but then fights." She has cool moments but they mostly come in cutscenes, rather than quests. Sylvanas had an awesome storyline in Wrath through a dungeon and a long quest chain. Yrel has moments interspersed in the wider campaign but it's not as concentrated and by and large extended quests have been abandoned by Blizzard in favor of dailies, dungeons, garrisons, etc. Never forget Wrathgate.

but I do like seeing Draenor before it was destroyed and comparing to how broken and shitty it is now.

Yes, the setting is interesting. The story is that orcs want power and get it through technology not demons, but that's just a set-up. The stakes aren't tremendously high because we don't see how things we value might be threatened. BC is demons invading, we know that goes bad. Wrath is the scourge attacking. Cata has deathwing destroying most of the world. Pandaria is a weird military campaign and doesn't actually have many stakes, since it's just a bunch of shitty bears on an island with some ghosts. Warlords has orcs who invaded, but the invasion doesn't feel like much of a threat.

So you combine that with the part where our interactions with the Iron Horde usually involve us going to them and it makes it hard to be invested in the story. Yes, the starting zones have a decent amount of plot where you are helping out a bunch of people fight off the iron horde and it's allies, but beyond that you are very much on the offensive.

Warlords could have been done really well, with each zone having an established base of operations that you have to bring your army to in order to have a fighting chance. Instead you set up a small base camp of like 13 people and then go out on a murder spree. This does not create tension.