I don't know if you have figured it out by now, but the trigger version of Solo Profound Darkness DOES have the XH difficulty. So you don't have to worry about doing it with endgame gear just complete it.
Seasonal UQ most likely won't ever come back due to PSO2 being pretty much abandoned at this point. It's a shame really because most of them were actually really fun and they would add more variety to the current set of UQ. They don't even need to make new ones, just reuse the ones from last year and it'll be already an improvement.
DF Persona uses 2 out of the 4 available mask when you fight him (which are based on the other 4 existing Dark Falz), it doesn't matter which version you play it'll always be just 2, and the selection is always random. When fight him as an UQ everyone on the 4 ships fights the same 2 set of masks. The hit-and-run attack you're mentioning comes from his DF Gemini Mask.