Imagine a hypothetical state of pseudo-sleep that causes us to withdraw during the night (the same as normal sleep), except we keep our eyes open/ stay alert.
We are just as hidden from predators, but now even more equipped to defend ourselves.
Therefore it seems difficult to deny that sleep itself has some form of rejuvenative benefit.
Please try reading my comment or following the thread. I'll paste it here : "I was specifically addressing his point about the drawbacks of sleep - "There are several survival drawbacks from sleep, as it leaves one vulnerable."."
In other words, sleep has rejuvenative benefits and it keeps us away from predators. Sleep can have many benefits. You can stay up all night, but you'd miss out on the rejuvenative benefits of sleep. Or you can safely tuck away and sleep and gain benefits of safety and rejuvenation.
Sleep wasn't a liability to our survival, especially our ancestors. It actually aided in our survival. Human beings who were active at night would have been the vulnerable ones as they would attract predators and were more likely to perish as a result. Especially considering out vision would be limited in the dark.
In short, sleep kept us away from the dangers at night.