I think it's more that there's a more drastic/stricter version of the Kurgan hypothesis that sees Yamnaya migration + Horses + Indo-European language spread as

I think it's more that there's a more drastic/stricter version of the Kurgan hypothesis that sees Yamnaya migration + Horses + Indo-European language spread as all one packaged good, spreading in a rapid wave from the steppe. Whereas this author is arguing that the horse part happened later. We already know the cultural-linguistic spread was more complicated than Gimbutas' original theory. That's not really controversial.