Wrathion's whole shtick in MoP was that he would do everything to prepare us for the Legion and presumably to fight the Legion back.
Then he ends up being more or less partially culpable for bringing the Legion to Azeroth, disappears for all of Legion and then pops back up. "Hee-hee. Yeah, I decided you could handle that Legion business. I figured the Old Gods were a bigger deal."
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then they honestly should've decided that to begin with. Regardless, he should've at least been around in Legion to help fight rather than just going "sup sorry I kinda helped cause the Legion, bye."