They don't rely on sexually attractive attributes, but attributes of which some happen to also be sexually attractive.
I don't like conflating attractiveness with sex appeal. There's an overlap, but they're conceptually distinct.
My claim is still that you can have attraction without sex appeal, and vice versa.
You can have attraction without sex appeal, but your baseline for what's attractive is always going to be sourced in what would've been straightforward biological sexual attraction if we were animals with no concept of anything beyond biology. So you can be sexually attracted even if you don't literally want to have sex with the person. If the two were completely independent, then we'd be seeing a lot more asexuals dating abhorrent-looking human beings, and that's just not observed.
That's why I used the term appearance - it's not about a one-dimensional beauty score. How you choose to present yourself, gives people an idea of how you like to be seen, and subsequently who you are.
This attracts certain people and opportunities, and repels others, which over time feed back into your personal development.
Yeah, but we're talking about beauty and ugliness. Not only "appearance." That's my point: you're getting off topic and bringing in objective factors like grooming habits, accessories pointing at political affiliation, assimilation and race which all exist outside of beauty. Ugly people can be well groomed, physically fit or average, affiliated with something you think is positive, and also a race you share-- and STILL be ugly aside from all of it which is why the comparison is irrelevant. "How you present yourself" is a choice that has nothing to do with your actual attractiveness and everything to do with your character, which can't be judged based on attractiveness; it can only be judged on your appearance ASIDE from attractiveness. So no, it's still not valid to judge people based on their ugliness AND if the aforementioned factors play into what you consider attractive, then it's still rooted in sexual attraction. By your logic, OP doesn't need to be pretty to receive advantage, they just have to brush their hair and not be over/underweight and they'd be equally advantaged as someone who looks identical to Adriana Lima.
It's a part of non-verbal communication, really. I think it deserves to be taken seriously.
Physical capability is quite easily estimated by looking at someone.
Mental capability is harder to estimate, but you can get a rough idea about preferences, education level, etc.
It's not about being intolerant, but making the best possible estimation, where real data is lacking.
It's about staying safe, and approaching the right people for the right things.
You keep bringing up objective, stand-alone traits when we're talking about overall prettiness and ugliness. An ugly person who is well groomed, physically fit, etc. can still be ugly, providing insight to positive traits while still having the face of an ogre. So if positive opportunities are given to people who are only conventionally attractive, you are still not accounting for the discrepancy in people who more or less fit a capability ideal while being ugly. And even then, you're also still ignoring the number of people who are rich and powerful while having bad faces, poor physiques, very poor grooming, and other 'indicators' a part of appearance that you think make or break someone's life enough that ugly people can be considered truly disadvantaged.
The only part of appearance that's separate from beauty + capability estimate standards & also consistent in these rich and powerful, is race (they're white). So the only arguable position in, societally, what types of people get what more easily isn't based on objective beauty, but just race. And no, I don't consider racist beauty standards to be "objective beauty" because it's not rooted in valid biological sexual attraction standards.