Is Pluto even a party player?
Ability 1: Her block generation is so damn slow. While it is nice how much Combo she has when those blocks are up, those blocks WILL be gone the next time she bursts. And then she can be block-less for a long time.
Ability 2: She has a pretty nice +Atk +Elem buff, but it consumes a block, has a short duration and long cooldown. Resulting in pathetic uptime and thus really only good for boosting your Full Burst turns.
Ability 3: She has damage cut, but suffers from the exact same problem. It's great-ish against Light (-50% damage cut for two turns is nice!), but against everything else the long cooldown just kills this entirely. Yay, you can save yourself from damage once. But it won't be ready for the second time, or even the third, so you'll just die anyway.
Burst: While it's nice to hit the 1000% burst modifier cap (or should I say 500% base + 500% modifier?) with ease thanks to blocks (starting from turn7), this is... pretty much all she does well.
Overall, I was impressed with Pluto when I rolled her, but now she just feels... off. She only has a place in the team for her high burst damage, which she does once per fight. I suppose if there was content that'd nicely cycle in 7 turns so that you could burst -> block up, it'd be nice-ISH... ... until you remember that her damage buff is too slow to keep up with that. But for now, you're either holding onto your abi1 until burst or bursting the blocks out and not having any for long periods of time.
Pluto just really needs an Awakening that puts her blocks outside of the 500% burst boost hard cap, speeds up her block generation significantly and lower the cooldowns of her partybuffs significantly. You know, so that there's actually be player choice on when to use blocks and when to save them for a higher burst.