Actually technically speaking WoD has the most content. It's just it wasn't very good content. Most of it (if not all, really) was just grinding dailies. A lot of people have been saying that WoD has little to no content but the truth is there tons of content. People just choose not to acknowledge it because they don't like it. MoP just had rep grinds and scenarios. WoD pretty much has the same thing but a little bit more of it with all the garrison stuff and all.
But yeah I do miss MoP. And no I'm not one of those people who were bashing on it when it was the new upcoming expansion because "WTF this is a Kung Fu Panda rip off". I was actually looking forward to it a lot. I miss it though not just because of the awesome Chinese theme to it or the music or even the story but because classes back then had more than 4 spells to use. With WoD they oversimplified the classes to a point where it's hardly fun to play anymore. It's one of the biggest reasons why I can't bring myself to play again until Legion and depending on how good Legion is I may never return back to WoW. Gameplay in WoW feels so boring anymore.
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Oh yeah, you're right. I can't wait to see people having nostalgia trips and saying how garrisons weren't actually that bad or that they missed questing in Draenor or how they miss bonus quests that you find out in the world or something. It'll happen with Legion too and the next expansion after that and the expansion after that. I remember when MoP was this joke to everyone and how it was such a rip off of Kung Fu Panda and how the Chinese theme didn't fit WoW somehow. Now people miss it and feel nostalgic about it already. It's so ridiculous and quite funny.