Here's the rule:
If someone is making money off their appearance, or otherwise directly capitalising on their appearance to further a career or for financial gain, it is okay to comment on their appearance.
In other words, if people objectify themselves for money, it's okay to criticise the worth of that object.
It isn't sophisticated. This isn't their ability because they aren't in control of their image. They aren't taking the publicity photos, directing the videos or designing album covers. And those things are unquestionably on the order of "She/he is hot, buy her/his crap." It isn't the act at issue because we don't see the act. We see the image constructed by people who own the creative output. Grace Jones was cast in Conan precisely because she would look good and strong wearing next to nothing. In other words, the decision was made in advance of casting to have the female lead be almost naked.
If they didn't want their appearance at issue, they wouldn't allow their beauty to be the central part of their image. Some people will take the "If you've got it, flaunt it" attitude, but then it becomes perfectly acceptable to discuss whether or not you've actually got "it."
We aren't talking about sex or beauty. We are talking about commerce. That so many people are confused about this illustrates why, consistently over time and regardless of the trend or target demographic, sex sells.