I agree on Cass and Steph (at least Cass's first three years). I wasn't super impressed with Simone's n52 Batgirl, but that's partly because I really dislike a lot of the artists who did it.
I agree that Larson's run, which I actually think started out okay, devolved after six months into a puerile, preachy, and ultimately really repetitive mess. And even though I liked Batgirl and the Birds of Prey, I completely agree that it wasn't as good as Dixon or Simone's work (though I liked it a lot better than the n52 version, which didn't feel like the Birds whatsoever).
Do you mean expectations? Because I do think that Steph and Cass set fairly high bars for writing and art, as do the original Birds of Prey run, Batgirl Year One, and several other titles featuring or starring Babs or the other girls. And whenever I ask someone if they really think that the Burnside or Larson runs match the previous Batgirl's, either they point to Babs Tarr's art (which was really good for the first trade, but it got a bit lazy in the last half of the run) or assert that the constant string of shallow villains and supporting cast are actually deep...which is not convincing to me at all.