“so anyone who can trace father to son back to Rashi.”
You’ll have a problem tracing anything to Rashi’s sons, as he only had daughters.
Joseph, I can see what you’re thinking, but as far as I understand Moshiach is someone who one wouldn’t expect it to be. Much like Dovid HaMelech being crowned was a huge surprise even to his own family. So, perhaps ZD’s prediction is more accurate than yours.