I think if he had argued that consciousness was a "transitional power source for intelligent behavior" it would all be cleaner. It is and was useful, but eventually becomes a bottleneck.
That reminds me of a Philip K Dick short story along those lines, The Golden Man. It's about a good-looking mutant who has no verbal abilities, but can see all possible outcomes up to a point in the future. He breaks free of containment, uses his ability to seduce women (also to escape), and in the end, the govt officials tasked with capturing him lament that he might be the end of the human race, if he has children with his ability.
It's not about consciousness, but the story definitely supposes that evolution can jettison intelligence if a better ability came along.
Most of conciousness's effort is working itself out of a job, making plans to train the nonconcious bits of the brain to do jobs. Training and kicking off mental simulations.
In more intelligent folks, that learning and training often becomes a non-conscious behavioral pattern itself. I study and learn mostly non-consciously. I was trained how to.
I think most people spend most of the time as philosophical zombies and that isn't something to be scared of.
Most of human brain activity is unconscious, yes, but p-zombies don't quite fit us imo, since they have NO conscious awareness by definition. I really feel it's meant to be a more present/absent distinction.
They're a good fit for Watts's aliens, though.