Except that the critique isn't really about this ad, it's about how ads shouldn't insult the people they're trying to sell to.
So for those of us who aren't reading "mundane to marvellous" as an insult, it's not critiquing the ad. It's critiquing a nebulous concept that ads shouldn't be insulting... but this one isn't, so where's the problem again?
This whole debate over the ad was started by the same person who spent several previous posts trying to push the idea that SE was deliberately putting poor-quality gear in game to drive us all to buying from Mog Station instead. They saw the ad wording and seized on it as further proof that SE was promoting their cash shop gear by outright saying everything in-game was "mundane" and not good enough. Which isn't being said in any way, shape or form.
(How many people would have even read the tagline, let alone absorbed it or stopped to consider what it was calling mundane, if it hadn't been pointed out and made so much fuss over?)