The problem of pulling in more younger guests gets brought up more less because people feel the previous subject matter was more mature, more because the current subject matter is actually something people know about.
No one (or at the very least, very, very few, and probably no children) was going on Splash Mountain FOR B'rer Rabbit. He was not meant as a draw. Whatever demographic liked him more was irrelevant.
They clearly want people to be attracted to this FOR Tiana, though. "You know this thing" is more what they lean on now. The demographics most likely to be interested in her or princesses matter more because they're trying to use them as a draw.
That's why people worry it might attract more kids that don't know what they're getting into. Not because of what they see when they get on. Because of whether or not it'll attract "oh, mommy, I wanna go on the one with Tiana!".