Learning a few more things from the various clans I don't really think any of that's the case, like the horses in Othard seem quite capable of keeping up to speed with men Au Ra riding them (Looking at the Goro and Noykin).
Heck the Steppes isn't even a traditional Steppes environment, the central parts seem to be more grasslands, but the Western Steppes feature several tribes who actively live in caves, more mountainous areas, coastlines, rivers, and deserts. It's a really diverse area!
While food might not be too plentiful though nutrition doesn't seem to be too big of a concern, one tribe manages twin births at a 33% chance, trade occurs fairly regularly between some tribes as well, heck there's even a tribe that takes pride in how much they eat and looking overweight. There's also reference of animals like goats, mammoths, tigers, and horses, which seems to indicate that things like animal fat and protein isn't too hard to get.
War tactics seem to be pretty variable as well, looking at the Xaela's in game stat distribution and the lack of mention of magic usage in combat, it seems they rely on a mixture of swarming, raw overpowering, archery, some javelin stuff and even some stuff with poison blowdarts. Even armor isn't completely unheard of look Qerel, who kill tigers with their own hands as a coming of age ceremony. Not every clan fights, but brute strength is definitely a wanted characteristic, looking at the Malqir's description "A western steppe tribe characterized by its unique leader-choosing ritual which, instead of the usual test of brawn, is a game of Kharaqiq--a chess-like game played on a circular board divided into three rings." The notation of a "Usual test of brawn" seems to indicate that strength is valuable, and it doesn't take too much of a leap in logic to assume that the "usual test of brawn" is well liked because "Brawn" is good for battle.
Even then, how would a tribe like the Buduga survive and succeed in battle if it was that much of an issue?
Lots of factors are still unknown, but the Xaela tribes deploy a lot of diverse strategies to survive in the steppes, I wouldn't discount strength as much as you do.