I'm a bit confused on what you're getting at and your timelines. Earth was around for billions of years before humans and had life on it the entire time except possibly the first few hundred million years.
"Earth before humans is in a death spiral" says to me they're talking about earth as it existed before humans, not life on earth at all.
Earth before humans died with the rise of civilization, and especially global trade. We transformed large swathes of land into farmland and urban areas. We enabled the transfer of invasive species throughout the world. We redirected and sucked rivers dry for our own purposes. We dumped our garbage and literal shit in waterways. We destroyed the majority of natural habitats.
And this all happened hundreds or thousands of years ago.
