She's more expensive (Merc Tax), her (0) push is only 4", her damage track (weak, moderate) compared to Graves is laughable.
That's not saying she's bad, by any stretch. It's that you have to build around her movement shenanigans more so than with Graves. To me she's not a direct trade out for Graves.
In a Pandy crew it helps a great deal to diversify your damage. If you get hard countered against your WP attacks (Von Schill, Marcus, Raspy) you'll be glad for the DF targeting actions in your crew. I'd be more willing to use Burt Jebson in place of Lust for that same reason. Of course those are 3 different models that do one thing similar to each other but do a secondary (or tertiary) thing much differently than the other two.
Lust has her place in a Pandy crew, the same way just about any other model does, it just depends on what you want the crew to do.