Reply #109: The point is, a female is not going to abstain in having a mate

[achtung_circus]

if she can’t get the cream of the crop

BUT

Does the plumage reflect a healthier male with spare energy to devote to display growth?
Does the better nest indicate available time from food gathering to devote to nest building?
Does the "beautiful" chirping mean that he is capable of defending his territory?

Does this result in a competitive advantage?

Yes.

Does this translate into better chick survival?

Yes.

That is how it works.