Can you explain why it's overrated, exactly? Game Freak is really pushing for Fairy-type to be well-known and liked. We're getting a bunch of new Fairy-types, and a few Pokemon like Jigglypuff, Marill, and Gardevoir who all have had sizable fan-bases at one point or another were retconned to have the new typing. A pure Fairy-type mascot legendary, a lone Eeveelution of Fairy-type with no secondary Eeveelution to hog the spotlight, Fairy being outright immune to the type that's been dominating the metagame for ages now... Dark and Steel never had this type of support back in Generation II's unveiling in comparison. Fairy-type is definitely going to have its share of importance this time around. Sakurai said he goes to the Pokemon Company and simply asks what's the current "hot-ticket" in Pokemon, and Fairy-type certainly sounds like it. I think Jigglypuff will actually be pressured by either Sakurai and/or Pokemon Company in terms of how a veteran fighter now syncs up perfectly with a new marketing agenda in Pokemon.
All of that doesn't sound overrated at all. If anything, the smash community is underrating just how much significance Fairy-typing is going to play for Jigglypuff. Without Jigglypuff as one of the first revealed Fairy-types, she'd be in the same position she was in Brawl, but with this timing working to Jigglypuff's favor, I think you can't just dismiss Fairy-typing as not a factor in this. Given, it's not the main reason she's coming back, but it's definitely a boost to her support.