The problem the Mongols did solve - though only briefly - was internal political faction on the steppe, allowing uniform recruitment and projection beyond it in all directions, to loot. (Every time a unified army left the steppe, it conquered something - nothing new in that). Once they had places looted, however, they had no remaining principle of unity, and broke up into separate hordes. When they conquered places, they brought a few traditions of steppe court life and changed dynasty bloodlines, and otherwise were assimiliated by the vastly more populace places they grabbed. When Tamurlane tried to put a unified empire back together, all he could do was loot various pieces of it in succession, depopulating them in the process, and leaving nothing.
You really need to read up on the history of the Mongol epoch, since you clearly do not know anything about it. One place to start might be Jack Weatherford's "Genghis Khan, and the Making of the Modern World".