I haven't seen a lot of her movies, but I certainly agree with you about Leon and Black Swan. Your basic premise may be accurate as well, but again, I haven't seen enough of her movies. Here's another view: Portman tends to be or bring out what the story asks for, nothing more or less, which is a fairly rare trait among actors. Meryl Streep, in contrast, normally magnifies whats on the page tenfold with her talent. (But you're always aware of Meryl Streep, even if you appreciate her overwhelming talent.)

Portman is the perfect manic pixie dreamgirl in Garden State, but the type is fraught with problems and the movie itself is extra bad, so it's easy to blame Portman for what is essentially Zach Braff's self-indulgence.