SCH solo of Sinister Reign without Helix II spells. Sequence of enemies was Arciela, then Rosalution, then Sajj'aka. To be fair, I did two-hour for Kaustra on Sajj'aka.
As soon as I finished typing the caption, I instantly regretted not including that it was a Trust solo. Indeed, that was my bad, and yes, they do help dramatically on the bosses with Ensilence or heavy physical attacks. Sajj'aka I honestly felt silly afterwards using august since he has no physical attacks at all.
In any case, the worst NM was Arciela, but she takes damage like so: During Bellatrix of Light, she takes significantly reduced damage from darkness, earth, water, and ice. And visa versa. So you must nuke INTO her Bellatrices.