Not your original objector, but ... I was willing to accept that early humans are dumb, but your explanation relies on evolution and not social interaction.
We know their brains didn’t grow much after birth, unlike humans, which also suggests faster maturity akin to living apes and likely less social support for extended adolescence.
Humans didn't evolve knowledge, they evolved the capacity to get more knowledge.
All the new knowledge they got they figured out from the environment.
Exactly. Humans didn't learn their way out of only having half a brain, more the opposite.