You're missing my point here, which is that mountainous areas weren't some peripheral interstitial zone they would occasionally mount expeditions to with a lot

You're missing my point here, which is that mountainous areas weren't some peripheral interstitial zone they would occasionally mount expeditions to with a lot of preparation and care. Rather, they were a core part of the Mongolian homeland and critical to the economic system of central asia. Mongolian horses were extremely important to that success, with good adaptations for the harsh environments and much better foraging than almost anyone else's. It allowed the Mongols to mount lightning fast campaigns across terrain no one else could, in conditions thought impossible. This was enabled by the incredible depth of experience with adverse, arid, and mountainous terrain possessed by Mongol commanders. If you want a specific example, look up the campaigns against Qara-Khitai, which famously included an expedition of ~30,000 over the Pamir mountains into Afghanistan in the dead of winter.