First off, I agree that vloggers/bloggers have a limited reach (even though Disney thinks it's an important enough reach to court with free stuff). But, your estimation is off since they don't have to reach every person in a family/group. Only the planner. So, if the top vloggers reached a million people, that would actually be a 4 million person reach (assuming an average of 4 people per family/group). That would then equate to 20% of MK attendance.
Again, not that I think their reach is that great. But as the military says, reaching the planner is a force multiplier.