Rideable Horses Preceed Agriculture

What if the domestication of horses on the Eurasian steppe begins much earlier (say at around the time of the domestication of the dog) with the result that they are fully rideable (in OTL it took several thousand years before horses were ridden on a regular basis - they were draft animals and chariot pullers in the meantime) at around the time of the advent of agriculture in the Near East?

Is this is a boon or a bust for civilization? A more robust draft animal and less isolation for the likely cradles of civilization is a plus, but the steppe nomads are going to be rather more competent militarily at a much earlier date which could lead to problems.

I think it might hinder the rise of agriculture and settled communities. Equestrian hunter/gatherers would have wider access to more resources and not be subjected to the types of resource constraints which made agriculture and urbanism attractive or necessary. Perhaps the equestrian adaptation would spread fast enough that sedentary civilization would not arise in Eurasia at all....until the urban state level civilizations of Mexico sent conquest fleets to Spain on 12 Reed 18 Monkey in the 1024th year of Aztlan