Earlier quoted context omitted.
The ground of your argument gets more swampy with each paragraph. It is visibly sinking. Coexisting for thousands of years, then suddenly wiping out 32 genera all in the same century beggars belief.
But did humans coexist with megafauna in America / Asia / Australia / Aotearaoa for thousands of years before they all died out? As I'm a New Zealander, I'm far more familiar with mass extinctions in NZ, and let me just say, to paraphrase a Smash Mouth song, well, after the arrival of humans, the extinctions start coming and they don't stop coming. For a few reasons. 1) Introduction of the kiore (Polynesian rat) - wh…
Island ecologies are fundamentally different from big continents, for obvious reasons. Even Australia displays island-like extinctions. So, yes, arrival of humans, with their animals, always has profound effects on islands. But that has little resemblance to what happens on continents.