Karen has Kayla, you (potentially), pseudo has Tom / is researching how to make him viable, and I suspect for the purpose of a measuring contest Emma would count as Karen's as well. Additionally, I think it's safe to say Ms Chang is subservient to both of them but we see her subservient to Barberry more since Barberry is a professor and is around more than Karen is.I know that power wise Karen is on par with Barberry but Zoe has her servants Ms Chang,Sydney,Jill,Becca,and the young girl you save with Rio. All together Barberry is more powerful and Naomi is arguably more powerful than Kayla is.
That said you are kind of right in that Karen is quite powerful but doesn't have the power base within the Coven that Barberry has. (And keep in mind Barberry has Kyle as well.) Though, if we were to include everyone who is one of your servants as Karen's servants, then we can add Lydia, Ward, Brittany, and a couple others. (I forget who else has access to the lights / is in the early stages and can be made your slave.)