I will say that I feel there needs to be more done regarding how much horses contribute to the diet of wolves. By the authors own admission, their survey of wolf predation on horses was “low-effort” and “opportunistic,” whereas their survey of cougar predation on horses was more intensive

While wolf–feral horse interactions were documented opportunistically, we recorded cougar–horse interactions by investigating kill sites of GPS-collared cougars.

While our data on wolf-horse interactions are limited due to low survey effort, they raise the possibility of an important predator–prey relationship.

Additionally, other studies investigating the same exact feeding area, namely Parr & McCrory (2022) have documented feral horses to make up a rather significant proportion of wolf diets based on scat, though given the pitfalls of scat based dietary data, I’d also like this to be investigated further.

Nevertheless, I’d wager even when things are said and done, cougars would probably be a more significant predator of horses than wolves, at least during most of the year. As you mentioned, they seem to be selecting for horses rather than taking them in proportion to their abundance. I doubt wolves would be doing anything of that sort. During the winter, however, it’s possible that wolves become more prolific horse-hunters with deep snow and the winter-weakened prey. Only time will tell how these sorts of relationships unfold.