It seems like in any population subject to evolutionary pressure, sexual attractiveness will inversely correlate with other kinds of reproductive fitness. If you see a peacock with a small tail feather, this is information that it is likely above average in other areas, because otherwise its genes would already have been wiped out. So intuitively, you would think that it would benefit individuals to find less conventionally attractive mates.
So far, I have encountered two possible explanations for this. One idea was that the things that make an animal attractive correlate with evolutionary fitness. I'm not an expert here, but it feels like the correlation here will diminish over time as soon as there is direct pressure to increase attractiveness.
The other, more convincing, explanation was that it is advantageous to produce attractive offspring. So, there might be a feedback loop here where if members of a population care about sexual attractiveness more, then attractiveness would confer a greater advantage, making attractive offspring more important, increasing the evolutionary pressure for individuals to choose attractive mates.
Can someone give an intuition (or better, the relevant math) for why these two latter effects dominate my original intuition? Or are there other effects at work here?