I haven't played WoD at all, but unless something has changed in the way they design their mythic fights those one or two new mechanics typically completely change the entire fight. They added things to A1/2 in Savage but it barely changes the flow of the fight at all, which is the issue. They're just slightly beefier versions of their normal counterparts instead of being unique encounters.
Compare, say, heroic (or mythic now I guess?) Dark Shamans, Malkorok, Thok, Siegecrafter, etc etc to their normal (or heroic now... these ridiculous name changes) versions and although it's only a few tweaked mechanics they completely changed the entire encounter and made it very challenging.
