I'm going to be honest, while I don't think is the worst character in the game, I think I've given up on thinking of her as a mid tier. She just doesn't stand out compared to the rest of the roster but unlike and who also similar in that sense, Corrin has worse mobility, initial dash, anti-camping game, recovery, and combo game so she isn't even as good as them and they are debatly lower mid tiers already. I'd argue that she is definitely bottom 10 and could be as low as bottom 5 if nobody picks her up and can rescue her from her horrible tournament results.
The character is mediocre, but not much more than that, and their low Orion score speaks more to their lack of popularity (Fates was a particularly divisive game) than anything else.
I'd be more worried about characters like Donkey Kong, who despite being relatively popular seems to have a poor performance.
Outside of this though, once a meme sets in regarding a character, it gets really hard to change that perception. This isn't new to Ultimate but is a recurring trend, both positive and negative.