To be fair, Deena doesn't have comparable material -- requiring showy vocal pyrotechnics -- and from divas Sheryl Lee on has scored via the totality of their performance, glamour, presence, charm, etc. The songs, oddly enough, are only part of the equation.
Whereas: Effie's material is the raw gut of the show, and it soars, in and out of context in such a way that it always cuts better. I bet Beyonce makes Deena work on screen (and I'm not much of a fan.) The bigger question, that's always been tied to this show: whose story is it, Deena's or Effie's? The show's arc supports Deena, but all of the emotion is in Effie's turns. Stay tuned.
"I'm a comedian, but in my spare time, things bother me." Garry Shandling