That was excellent. He also had a great take on Batman in Wednesday Comics.
Alan Moore generally has the reputation of being the best comic book writer.
There is going to be some disagreement on this, and an anti-Alan Moore will stand out more than someone arguing about his strengths.
An advantage Moore has is that his political views align with those of the people writing about comics. The Mary Sue or Vox aren't going to criticize him for being too far-left.
There can be an argument that Frank Miller has become underrated because his views have put off people who write about comics, even though it has nothing to do with the quality of the work that earned him his reputation. There is also a philosophical difference in assessing quality, depending on whether you look at averages or whether you look at the best work. The former approach might penalize Frank Miller for not getting hit by a truck in 2000, which is one reason I personally prefer to consider the reputation of an individual based on their best work.
If Grant Morrison is the tenth best comic book writer ever, he is probably overrated, given all the talk about how he ranks even higher.