Reading the abstract is a lot more pleasant than the article, which rambles.

Sounds like the author is supporting a theory that horse-riding spread along with Indo-Iranian languages (Sintashta culture) rather than earlier. Which doesn't seem crazy to me.

Horses were definitely livestock for a long time before that, kept for meat and dairy. They were very useful on the steppe because unlike cattle (which were imported from elsewhere), they can dig through snow to forage.