What you talkin bout TM? That past stuff is super important! That's like saying..... finding out the past of Noel and how she became a Murukumo Unit isn't important to the story
Except Noel is the main heroine and Platinum is the most worthless playable character in terms of storyline, she only has worth because the soul of Trinity is in her Nox Nyctores.
Even Makoto has more worth, she's atleast a part of the current events, what's Platinum doing? Except for looking for Bang and irritating Ragna.
The past stuff doesn't make anyone anymore important unless it effects the current events or leads up to some sort of plot twist.
Being responsible for Nine's demise is a interesting point but saying her importance "sky rocketed" just for that is just wrong lol.