Although everyone is trying to be helpful, nobody seems to get that the question is whether or not the priority drops apply to the factory as well as to the store recruitment, regardless of XiFeng's factory availability. Well, I'll find out in just under two hours, anyway. If it's Lin or another Meiling, I'll assume it's because the priority actually does apply to the factory (which isn't exactly scientific, but yay for confirmation bias). I'll post the results when she emerges.
Nope, it's actually removed, support ticket response stated it was noted and will be fixed in next patch.
Priority applies to store only, I'd think (it would make sense given Nutaku's record; example: Priority Rate boosts in games like FKG, MWA, etc. the free gacha does not get any boosted rates, only premium)
I dunno about MWA but just every other game I've played didn't have highest rarity girls in regular gacha. The only one I can think of that has besides this is Crystal Maidens and it doesn't even count at this point.