Not sure she's highly regarded acting wise, but Mila Kunis is barely average. She's right on the cusp of average. Natalie Portman is another. Never been impressed by her acting skills.
I don't know most actors/actressess are rated about where they should be. Tom Cruise is probably the most overrated actor but only because he gets paid so much and has been around forever. I don't think anyone thinks he's Olivier or Oldman.