I've already said that I would consider both Winstead and Smollet-Bell attractive in a fairly standard way. Many people would.
But as in everything in life, there are levels. Winstead and Smollet-Bell have both been around for years, but dudes ('male gaze again, sorry!) do no lust after them with the same intensity that they do a Margot Robbie, and never have. Or an Alexandra Daddario. That's keeping it real.
Margot knows there are levels to this thing as well. You put Margot next to Daddario or Gugu, suddenly she's no longer one or two levels up on the sex appeal scale. She might even be half a point behind. In that sense, Winstead and Smollet-Bell are safe choices for Robbie...attractive, but not so attractive that she's no longer the most obvious choice for sexiest Bird Of Prey.
The less said about Rosie, the better. Margot had casting power and didn't want real competition. It is what it is.