The fact is that the actual original territory of Russia is up to Tatarstan, the former Kazan Khanate. The Urals and Siberia in tsarist times were not considered Russia, prisoners were exiled there from Russia.
First, you need to understand what a state is. All the countries are states. They are states of mind. Your state of mind regarding borders might be different from that of the next person.
Whose state of mind is right regarding Siberia? Isn't it the one who maintains the power over it? Written words regarding borders are only there to keep the memory of who claims ownership of what alive.
If you or China or Mongolia or anybody else doesn't like the FACT that Siberia is part of Russia, go take it from them if you can. Your borders might be right. You might have the strength to do this. If you do, you can make Siberia belong to anyone you want.
Firstly, Siberia belongs to those peoples who existed there before the conquest of Siberia by the Russians, and not to the Chinese or anyone else who, according to your concept, should conquer it. Secondly, the indigenous peoples of Siberia have every right to independence, like all peoples on planet Earth.
The current maps say otherwise about who owns Siberia. Take a look at popular Wikipedia maps. They show Siberia as part of Russia. Who would benefit from Siberia being part of Russia? Russia of course.
This seems to suggest that Russia is taking over the world through some unknown means and methods. They certainly didn't conquer the map-makers to make the maps change. Maybe they rule the world and we don't know it, right?
If Siberia belongs to the indigenous peoples of Siberia, let them prove it by showing it on the maps... if they are strong enough. Or is it that indigenous peoples of Siberia rule the world, and are simply letting the maps exist as they are as a cover for their covert operations?
I agree with you that what is right isn't always the thing that exists. The indigenous peoples of Siberia might be the rightful heirs to Siberia, and they might think that they own Siberia. But what do they have for strength if any other country decides to push them off their land right into the ocean?
Once upon a time, many colonial peoples of the British Empire, and recently the Soviet Empire, did not have their state on the map. The time will come and the states of the Ural and Siberian peoples will appear on the map: Tatars, Yakuts, Buryats and many others.