1. Neither the premise of spreading genes with "little effort" nor the bit about incentivization is actually true unless you have a very odd definition "less time". While lifelong monogamy may not be an obvious strategy, communal child rearing that involves fathers has been the norm for most of recorded history in all civilizations, with poor and absent fathering nearly always being villified unless needs of the community outweighed it.
2. Lots of women have multiple children, no problem. Many elect to go back through it again. This idea that pregnancy wracks every woman is just ridiculous.
It's not even clear we evolved that way. Looking at our near genetic relatives, they don't actually do things the way you're describing and communal living isn't "a group of females desperately trying to avoid pregnancy as males raid and ravage them."
In summary, men are more likely than women to be reproductively successful with a low effort child rearing strategy. Is it the best strategy overall in modern society? I don't think so, but you can see how we'd evolve that way.