Sexual selection is different than what is "needed" by a species. Males who are able to fight off others and therefore are the exclusive mates of a large group of females will propagate the genes that reinforce their physical prowess and aggressive behavior.

This also benefits the females if they will have sons who are more likely to win their own harems.

But there are also competing strategies. Sneaky males who can mate with another male's group without fighting him off will also propagate their genes. Females in the group benefit if they will have sneaky male offspring who will be similarly successful.

"Strong" is not the default for "most likely to have offspring." There are many strategies, including monogamous species which invest together in their offspring. Evolutionary psychology can get oversimplified and misapplied, especially by beta males whose mothers hurt their feelings and now lash out at women whenever they get the chance. That last bit was an attempt at irony, btw.