Center of power hardly could be within a spitting distance of the border with a much stronger neighbor (the Golden Horde) or even just the nomadic raiders.
Again, important not to understate this point about nomadic neighbours: people were captured en masse all the way into the late 19th c. and in the 15th/16th c. yearly losses from frontiers were in the tens of thousands, some years much higher. Some of the prisoners were recovered or ransomed, but most were sold onwards into slavery elsewhere.
I mean, there are cases of Peter's soldiers who got captured and enslaved by Crimeans or Nogays from right under Kiev into the 1730s.
Hmmm, I was thinking that the POD could be which capital the Mongols decide to let collect tribute from the other Russian city-states. So instead of Muscovy, Kiev gets the honor and can skim off the top.
I think you overestimate the stability of medieval governance in general (overlords in Europe could be absolutely brutal and predatory too) or the reliability of the Horde as an overlord. Moscow (and other cities in the Vladimir Grand Principality) might have won the yarlik and even supported the Great Horde on occasion but that didn't stop it being raided and attacked every time some internal politics in the Horde made that politically feasible.
The theory on why Russian government is so brutal says that Moscow is not on fertile land and so needed to exert extreme control over the more fertile lands and its expansive hinterlands. But if the center of power is also where the best agricultural land is, perhaps Russia's culture is less coercive and brutal.
What I describe above was obviously the case in the high "Kievan" middle ages too and in fact despite the complex and sometimes cooperative relations with the Cumans and the Black Hats, their constant disruptive activity led to Russian settlers from the Kiev/Chenigov/Seversk region to migrate northwards into the supposedly "not fertile" Zalesye, long before the Mongols appeared on the scene. And in the 14th-15th cc. that pressure still continued and people were migrating towards the White Sea away from the Zaseka line/Wild Fields.
Only constant government effort and a booming population reversed the situation and kept the expansion of 16-19th c. Russia going INTO the steppes against the Kazakhs, Nogays, Kyrgyz, Kumycks, Kalmycks, Oirats, Crimeans and other Tatars and Caucasian peoples , as opposed to the other way around. If you want to know what the impetus for early centralization was, you should probably look there.