" Looking good makes people feel more confident because it feels good to be the "best" version of yourself."
Yeah, to be seen as by others.
Did you even read your original comment?
You said "The "self-confidence" any girl gets from clothes and makeup is from being seen as attractive to the opposite sex and also from being seen as moreso than her peers".
That is demonstrably false, because pretty privilege applies across genders and sexual attractions, and humans like to look good for innate aesthetic reasons. You feel good if you dress good, and there are studies that show this for people without any social interaction.
It's not (just) about being attractive, it's about being more confident that you have value. Kinda fucked that humans innately place value on beauty, but we do.