The reason why Pluto is considered important is that at later difficulty content (think AQ5, the incoming actual ragnarok disaster (one level up than our current ragnarok disaster, the current ragnarok disaster gets renamed to ultimate) is her ability to damage cut.

Damage cut ability now doesnt get used much as most people can survive with -50% atk down and one damage cut ability (e.g. joan's or gaia's, etc), but game like this is bound to have power creep, and that's where stacking multiple damage cut ability (including defense buff) will help clearing higher difficulty content.

With that said, it's still 1 year ++ thing for us, so no need to push that panic button... yet..