Short term maybe. Long-term absence of fathers leads to increased jail time and other negative outcomes, which could affect long-term success:

https://www.mnpsych.org/index.php%3Foption%3Dcom_dailyplanet...

Promiscuity isn't a novel invention, thus it likely isn't beneficial overall if it isn't widespread right now.

A society that allows that will collapse when too many people are bad players.

It it also true with societies where men aspire to have 4 wives each. These are societies with too many single men, and a tendency to be violent.

Having children with multiple partners has always been and will always be the quickest way to spread genetic material. That is true regardless if women are having 2 kids or 5. Speculating that lower birth rates will somehow increase absentee fathers is baseless, that evolutionary pressure has been present since before we were human.

You are getting downvoted but in 2021 that’s precisely who is having the most children in developed countries. If you look up birth rates by income bracket the trend is clear: poor people and broken homes birth more children than wealthier professionals