It was definitely the crappy leak's fault, the art style didn't match Bravely Default's and you can't rely on stylistic stuff to be signifiers when it's an anime style. If someone made an off-model close up of Shulk, Marth, Lucina, or Roy, you'd likely have the same reaction of people not knowing who they were meant to be.
Yeah, it was funny. I remember people thinking Geno, Agnès, or Neku were more likely SE reps.
That's true, but if we got a unique newcomer from Street Fighter, it'd be Chun-Li..and I have little doubt that she'd be in before Ken if she could be an echo..people would also likely say Chun-Li is more iconic, important, and recognizable.
This isn't about importance or recognizability, it's about popularity and Shadow is more popular then Tails and easier to do as an Echo..kinda like the possible reason Luigi got in over Bowser, he was a popular, easy clone.