80,000 years may be a blink in an eye in evolutionary terms but it does not take that long for a predator to come into an environment and become entrenched as the natural check on some other species.
I would say https://science.sciencemag.org/content/314/5802/1111 for example of introduction of species
something like this https://www.journals.uchicago.edu/doi/abs/10.1086/285705 for how dominance of predator works.
However not sure how well the Native Americans were actually keeping animals in check given the many species they have been shown to have helped bring to extinction.
That said not sure how long it would take from being a natural predator to being a keystone species.
One doesn't need to be someone's long time natural predator to have an impact
The fallacy that, IMO, we are falling into is (ironically) caused by scientific reductionism... the simplest explanation is probably the correct one. This doesn't work as well for the evidence types paleoanthropology has to work with.
Take Israel or Morocco as a comparative example. There were sapiens there before Neanderthals, but they are not thought to be ancestral to any modern people. The majority are not. This makes intuitive sense when thinking of species or subspecies (eg Neanderthals), but it works the same with populations.
Also, it's easy to think of ourselves in permanent "infinite growth" mide, where we colonise and dominate. But, recent years aside, humans bloomed and receded just like other species. Range expanding and contracting.
Just because a population is in the same place does not mean that it's ancestral. The first, second or eighteenth population may have no current ancestors... or none in that area.
As Dawkins puts it "descendants are common, ancestors are rare."