Terraprisma. I love watching this thing, but it's so ridiculously strong that I don't actually get to see it in action since it kills things so quickly, and Empress is so late in the game that there aren't very many things I really get to use it on. Moving it far earlier in progression (and nerfing it accordingly) means it'd kill things slower and I'd have more content to use it on.
Sure, I could refight earlier content with it, but then we're back to the first problem where it annihilates everything too fast for me to watch it for long; even a Broken Terraprisma is still going to eviscerate invasions and previous bosses.