good point all on Rashi’s daughters – totally forgot about that.
As far as coming from undistinguished lineage, although Moshe rabbeinu was raised in pharo’s house, he also was the son of Amram who seemed to be one of if not the preeminent gadol hador at the time. So even if mashiach’s background will mirror that of Moshe Rabbeinu’s, coming from distinguished lineage isn’t necessarily a stirah.