They don’t need cows, but praries evolved with bison. There’s positive effects on carbon sequestration from short, intense grazing, much like a roaming herd of bison would have done. It’s not just removal of grass, it’s also nutrient cycling, enzymes in their spit stimulating additional growth nodes, hooves causing disturbance and pressing seeds into soil, all kinds of neat stuff. That’s NOT the same as cattle on public lands. It’s also not the same as fire, even though fire is awesome.

For reference, I’m a prescribed fire practitioner and manage a chunk of grassland with primitive sheep.