I wonder what Russians would think about that. Are we implying that Russians were less civilised than the Turkic Khanates, Uralic tribes and Caucasian Kings?
No. It's like the Chairman said, a question of cultural superiority, but numbers are also an important factor. Russia proper was never really conquered by foreigners, they just paid tribute to the Khans, so assimilation doesn't even apply.
In the "Mongols conquering China" example, China was clearly more advanced culturally than the Mongols plus the Chinese were outnumbering the Mongols by far. Same for the Mongol conquest of Persia or later on the Arab conquest of Persia, huge populations with advanced cultures always absorb more primitive conquerors while big populations with less advanced cultures often adapt to the conquest culture.
That's why Gaul was heavily romanized after the Roman conquest - Roman culture offered a lot of opportunities to the Gallic nobility -, but not germanized after the Frankish invasion - Frankish rulers were just a small elite in an otherwise more advanced territory and adopted the Romance language and culture of the people they conquered.
The Anglo-Saxon invaders left a huge impact on the British isles because there were large scale migrations and culturally they were about even with the celtic inhabitants (Roman influence on Britain had diminished at the time). The Norman conquest left a big impact on language and culture because the Norman culture was more advanced, but it ultimately didn't change culture that much, because the Normans were only a small ruling caste.
According to Russian patriotic websites and books, Westerners have always regarded Russians as uncivilized barbarians that should be exterminated because they occupy territories full of natural resources. Also, Russian patriotic websites and books describe all Westerners as degenerate uncivilized barbarians that have no culture and any morality whatsoever. They often provide somewhat strange examples to prove their words - for instance, an article that I've read once claimed that the fact that Western languages (especially English) don't have as much diminutive suffixes denoting affection as the Russian language proves that Westerners are culturally inferior to Russians (source).
I can't read the article, but the argument seems pretty stupid. In German you can also use lots of diminutives if you want, but I'm sure the authors don't have a kind view of Germans either. Though it's not entirely wrong that western people historically have looked down on Slavic people as less civilized and - when racial theories came into fashion - as inferior. Which is why I find the very active Russian Neo-Nazi movement (the Polish one too) so ridiculous, in Nazi racial ideology Slavs are ranking pretty low, beyond the blonde ones that could potentially be germanized, they were thought of as potential forced labourers at best.