Ultimately, being able to attract the interest of a partner is directly connected to better survival in that offspring that are actually born have a better chance of surviving than those that never have the opportunity....it's just the thing that attracts that partner may not contribute to survival after they are born.

They certainly can be, for sure, though sometimes the mechanisms can be blurred - for example, is a sexual preference for greater height in place because taller people are inherently better at something because of the height OR is it simply that people with access to sufficient food and nutrients (through a variety of mechanisms) are taller, thus height is just an indicator, rather than a survival mechanism itself. And that doesn’t even begin to account for sexually selected traits that are theorized to be technically detrimental to day-to-day survival BUT that kind of indicate to potential mates “if I can afford to waste energy on this useless trait, imagine how awesome I am in everything else!” (eg peacock feathers).

In other words, sexual selection can be weird to untangle.

Sexual selection complicates attempts to explain certain evolutionary changes - sometimes, a trait just becomes more attractive to the other gender and, while that trait may represent an underlying superior fitness (beyond the obvious “can have more babies because I’m more fuckable than others”) it also may not. It’s possible that early humans just decided they weren’t down with hairy boning so much.