Inquisitor said that Kanan performs Soresu at ridiculous degree, and he is a poor student, that is probably dun moch but I doubt that Kanan is a mediocre jedi master level either, so Inquisitor shouldn't be that good, he is not a Sith and his power can't be on the same level with even Ventress, otherwise Palpatine would sense his power and commands to Vader to destroy him, just like he commanded to Dooku to do the same thing before.