Harry has a few friends and some connections. Christos must have much more to force a membership in the senior council like that.
The relative potential impact of Christos' constituents backing him, and Mab backing Harry in situations where he is
hers and an insult to him is an insult to her, seems to me to skew in favour of the latter.
I don't think Harry could bully his way onto the Senior Council any time soon, but he is better positioned than any wizard except Eb to tell them to go whistle if they lean on him for something he doesn't like.