I am absolutely not sure about that. At the times when humans still had to hunt for their dinner, and had to take care not to become some raptors snack either, monitoring was an essential part of surviving.
Those examples are not exactly on the mark. Humans are great at
visually detecting movement, and we've effectively used that skill to hunt and to prevent from becoming dino meal.
But in IMC without outside visual reference, we're very bad at detecting a slow uncommanded roll, a gradual loss in altitude, deterioration of speed / energy, etc. All items which should be part of any pilot's basic instrument scan.
We've had many many examples of these kinds of failures over the years. Eastern Airlines Flight 401, the Asiana crash at SFO, the recent AirAsia crash in Indonesia, etc. In each of these accidents none of the multiple crew members detected that something was wrong until it was too late.
If we only rely on pilot monitoring to detect slow deterioration of aircraft state, then accidents like above will continue to happen. Even if the FAA mandates additional training, hand flying, etc., it's human nature that we're not very good at certain tasks. So I think there is a diminishing returns in FAA's approach to monitoring.
Alerting -- automated callouts, warnings, etc., is part of the solution. But sometimes we're good at ignoring those, too.