There is a colossal difference between Grandmaster and Revered Rank. Dumbledore is leagues above everyone else. Just so you know, there is no Grandmaster wizard with an MP value greater than 165,000 Flamels
It turns out that squibs do not have magic at all, and therefore they are no different from Muggles, but then why do Muggle-repelling charms not work on them, etc.?