Alt-text: "I really like the name 'Alistair'. It's terrific."
To reach a certain grade in the Mages' Guild, you have to pass a theoretical and a practical test in several disciplines to prove you are capable of using and managing magic power of that level.
Grade 4 is pretty average for an older mage in some higher position, but not exceptionally good. Katharina also being 4th grade means she is actually remarkably capable for her age and experience. Still, she calls Coumi "Master", because that's how you call the leader of a guild house.
Updated on 2017-10-28: I still think Alistair is a great name. When I hear it I always think of the grey warden Alistair from Dragon Age, and the malkavian Alistair Grout from Vampire: Bloodlines ...