If that would be true then there would not exist any pair bonding species, and there is some excellent benefits from it. Two parents mean one backup while raising the children, and two parents is double the parenting. Two parents also give some potential benefits with twins, something which pair bonding species tend to have a lot of while non-pair bonding species don't. The primary argument in favor of pair-bonding is that having a lot of offspring that don't reproduce is worse than having a few that do.

Humans with our great variations of behaviors has both pair bonding behavior and non-pair bonding behavior, with genes that code for both. If one strategy was always superior to the other then we would have settled for it a long time ago.

(Its a law or something when talking about genes that the behavior is always a gene-enivorment interaction, and there are likely many more factors that influence pair bonding behavior).

Maybe not? It doesn't much matter if you have a lot of offspring, if the offspring don't survive and reproduce. It's an optimization problem of having enough offspring and being able to ensure that they survive to adulthood.

The only people who can historically get away with that are high status men (less so women, since child bearing is intrinsically metabolically and temporally expensive). Globally/long run, it's not a great strategy, certainly not compatible with modern ideas of liberty.

If life gets easier and easier (e.g. government guarantees housing, income, education, etc.) then I can see that becoming nearer the truth.