Well, maybe I didn't say it correctly.
You are right, Legion was being developed during 2012. But, I think they were only talking about How legions story would go into WoDs when Mop was around.
And then, when WoD was in it's alpha phase, legion was being designed on paper and characters were getting drawn and everything was going well (As seen on the looking for group documentary before WODS release at blizzcon 2014).
That's why WoD was NOT a good expac, for 3 reasons.
1. It's an AU story, so...of course it would fail.
2. Because of all that legion stuff, blizzard thought that legion should be focused more on because A. The legion is a WAY MORE interesting threat than just more orcs, and B. it's on OUR azeroth...not some...random ass planet that takes place in an alternate universe. Look, i've know half of those guys already....and our draenor is perfectly fine the way it is, destroyed...I don't care about that place...I care about my titan infused world (Spoilers....shhhh).
3. To many orcs....So....MUCH...orcs...FUCK EM! 14 months of hell, now....Iron....FUCK!