Depends on what we're debating. Are we debating whether or not humans need sleep? Or simply that beings with similar brain "design" need sleep? Perhaps due to a flaw in our (Animals) common ancestors we developed sleep to overcome other negative traits. Which is to say that sleep is simply one flaw to compensate for another flaw.

Given the path evolution takes it seems a stretch to ever consider it best, perfect, good or anything other than "it worked just enough at the time". Just enough being the key. All we know is that sleep didn't disrupt animals enough to entirely fail the evolutionary test. However plenty of garbage features go along with more powerful features. One in isolation is not proof of it's perfection, I would think.