I read this post a couple of days ago and did some experimenting. only with VR UQ so far. Static: Same character and lvl (Bouncer 76/Hunter 55). it was also the same UQ time frame ie I did the UQ twice for the allotted time. difficulty I think was XH (lvl 85). 250% rare drop boosts 100% tri. 50% tri from daily 0% party differences, in the first VR UQ, I went for stringing as many combos as I possibly could, along with variance in PA's as well as switching between soaring blades and jet boots. since I'm new to the whole PSO2 universe, I'm still trying to figure out the nemesis/slave GIX etc. but what I can tell you was that I got 3x13* weapon drops as well as a drop. I have yet appraise them so I guess I'll find out today what they are. with the second I spammed a single PA from soaring blades. and got 0 13* drops.
My conclusion: stringing combos and total dmg to during the UQ play a big part in rare drops. Honestly it was one of the first times I got 3 rainbow rare drops with one shooting the rainbow into the sky assuming its an Ultra rare (lol, don't know how else to describe it) though I need to appraise all 3.