■Judge on the image, the things you shouldn't focus on: BD, SJ, all B-Rank battlesuits.

■Also in the same image, SP (Mob-cleaning DPS which's still relevant till today), YA (need the core - Augmented version is one of the current best supports) are ones you should focus on for now. Once SP and DK (augmented YA) reachs to SS Rank, you can leave SP for a while, but you have an option to further invest more for DK to SSS Rank with 6☆ Core for easier Shield Reset.

■About the others:

SS-Ranked SS's Ultimate will make enemies take more Physical DMG, which's also make her useful as support, aside of her freezing ability from many skills which's proved to be useful against Huodou if played skillfully.

SS-Ranked WD's Elemental Shield will boost Elemental DMG for team without needing her to enter thr battlefield.

SS-Ranked FS will have 5 bars, and each bar will boost dmg for her for each successful combo atk.

DP, is the one you can leave at A-Rank as her's off-field impair is good enough, but the higher the rank, the better performance.

UR is still useful against some bosses, such as SK. But, she's not too bad, but she's not too good either.

VR, if she has the core, then she will become VD. But VD is heavily relied on Tranquil Arias as well as CH to be good. In late game, "is it just me or she isn't longer good like she used to? Idk"

About HoV, although she's still good in this day, she needs Key of Void as well as whole Sirin A Set to be good. But perhaps, you will only need that Key then any stigmas which's not only boost melee dmg.