Does anyone here use grader.website.com on Hubspot? It perplexes me that my site receives a much higher grade then my competitors, yet their page rank is highe

Does anyone here use grader.website.com on Hubspot? It perplexes me that my site receives a much higher grade then my competitors, yet their page rank is higher (we have more inbound links then they do). Is Hubspot's grader reliable?