At this point, leveling your assault skill on your primary team should be your primary goal. That's where your gems should be going, especially if you can't clear Advent Ultimates yet.
I can clear experts with no problem, Ultimates take a bit of work, and I have yet to clear an Advent Ragnarok. Is there a better (read: easier) way of upgrading skills than just brute force 10x normal gacha-ing and throwing all the results at the primary team weapons?