There are many past ecosystems we could choose to attempt to restore. Certainly Yellowstone had its wolf population. But it also had a native human population, whose practices affected the ecosystem.
Do we want to "rewild" to before European settlement, so re-introduce Native American land clearing practices? That would certainly help restore the quaking aspen population. Remember, there was 11,000+ years of humans as one of the top predators in that ecosystem.
Or do we return it to pre-human habitation era at the end of the last ice age? That's what truly "wild" means, no?
Ars Technica appears to have forgotten. They write: "So when they disappear—largely because of us—there are myriad negative effects, culminating in a lack of biodiversity."
Who exactly is this "us"? It can't mean "humans".
To really rewild to pre-human times would call for a return of the megafauna like the American lion, the short-faced bear, and the other animals that disappeared some 11,000 years ago.
But that's not what most people mean when they talk about rewilding in the Yellowstone context.