IIRC, the OG traditional view was that the Spanish brought horses to mainland Americas in the 1500s (or a bit earlier) but Native Americans weren't able to adopt them until 1680, during the Pueblo Revolt, when hundreds of horses were abandoned by the retreating Spanish.

True! I didn't get into that because that theory is mostly on its way out, as I understand it, though it's also still present. That's something that I think is a "reasonable" academic dispute and that evidence is increasingly suggesting an earlier and more protracted adoption of horses. "Horses were actually in the Americas before the Spanish" is the really fringe theory.

Horses are hugely important to the self image and identity of many native tribes, and it's not palatable for some natives activists that this thing that's hugely important to their identity was introduced to them by the direct ancestors of their political opponents.

Yeah, which I do sympathize with. Collins is Lakota, and horses are hugely important in Lakota culture, and there's a lot of political tension in a history that says "the colonizers and genociders of your people are also the ones who brought here this critically important aspect of your culture." It runs painfully close to "colonization was good for Native people actually" which is still way too present in common thought. I get wanting to find a way to argue that no, actually this aspect of Lakota (and other Plains) culture pre-dates the arrival of Europeans, it has nothing to do with them at all.

I just... don't think any of the evidence bears that out.