A spear point that is stuck in and broken off might remain in the carcass.
A band of experienced humans with spears can take out any contemporaneous mega-fauna without much danger at all, even a mammoth.
Mega-fauna that developed alongside humans developed a fear of them. It is likely that much of the mega-fauna that went extinct at the same time humans showed up never developed that fear. We have seen the impact of an invasive species can take place rapidly, before any local animals have time to adapt.
Much of the mega-fauna on the list seemed to be doing just fine until humans showed up, then they were gone. Have any citations for them being in a long term decline BEFORE humans made the scene?
But that’s precisely my point!
Why is it specualted that specific Mega Fauna went extinct because of human hunting, but the same did not occur in Africa or Asia at the same time with a greater - perhaps more established human population.
It doesn’t make sense.
As far as a flensing tool - yes, I imagine that a few of the tools broke-off in the hide and bones of the animal.
Finding a handful of spear-points in or near a few dozen carcases is not evidence of mass eradication at the hands of human hunters.