Furthermore, I don't see any reason why that state of conscious awareness would need to have been significantly different in my pre-human ancestors. Would a Homo Erectus have had a significantly different sense of experience? An Australopithecus? Our common ancestor with other apes? If so, why?
It seems to me the parts of the brain active in that state correspond closely to those in other mammals. Yes when I'm solving maths problems, writing a HN post, playing a board game or solving a crossword puzzle I'm using higher brain functions that other mammals don't have. Sure. But what has that got to do with conscious awareness? I have that when I'm doing things very much along the same lines as activities of other mammals. Running a race, climbing a tree, walking through woodland, stalking prey, experiencing love, or loss or panic. I don't see why I would expect their experience of those things to be much different from mine.
There's no 'animal mode' state of awareness that we have when doing 'animal' things that's a vestige of our pre-conscious past. Conscious awareness isn't something that only kicks in when actively engaging higher brain functions. So surely that is evidence it's a foundational part of our mental heritage, not a modern addition?
It seems to me that arguing that a higher mammal's experience must be dramatically different from mine when doing common activities, to the point that it's impossible for us to even imagine what that experience is like, is the extraordinary claim.