The indigenous populations of the Americas (north and south) was somewhere well under 112 million prior 1492
That is such a hopeless argument. For one, you do not need a lot of humans to drive megafauna extinct. Not any more than you need a lot of snakes to drive flightless birds extinct on an isolated tropical island.
More importantly, this happened long, long before 1492! Some 13000 years before. The population in 1492 could have been a billion or it could have been one for that matter, but either way still wouldn't have proven or disproven the overkill hypothesis.
I never believed the hunted to extinction nonsense.
People, especially anthropologists who live with native people and/or devote themselves to try to understand their way of life on a deep level, are understandably reluctant to believe such disheartening things about their study subjects. Some of them argue passionately against it, but that is one of the times you need to look a little critically on their actual arguments - especially the things they can't explain.
If humans did not contribute decisively to killing off American megafauna, it was a fantastic coincidence of timing.