My Polish friend, you have to understand that as a historian your historical views are coloured by the perspective of your own nation. Let's go through a few examples.
later illegally annexed into the Soviet Union.
Let's be honest here, possession is nine tenths of the law. The idea that Stalin's puppet governments who joined the USSR are less legitimate than, say, the post-WW2 French and West German governments established by US occupation is purely arbitrary and based on modern self interests. For Russophobic types — and frankly, PL Commonwealth descendants are irrationally Russophobic and seem to have forgotten what they themselves had done to easterners in the 17th century that started the fight in the first place — everything the Russians do is illegitimate. We have no obligation on the other side of the world to agree.
China is "post-Mongol" as historical maps show a clear shift that occurred under the Yuan dynasty which was as pivotal for China's history as Qin
The reason why this happened was because Mongols were like Vikings rather than Romans. They raided and plundered and took tribute but never established their own state structures because they had none to offer. That meant that Mongol vassals were worse off in all aspects after the Mongol empire withdrew
All Chinese historical chronicles since the 1270s (Mongol-supervised) and 1360s (Han-supervised) list the Mongol Yuan as a legitimate dynasty of China and part of its lineage of succession. The Mongols, by constructing the Ortoo Yam, a highly advanced and well regulated network of trading and full-time messenger relay posts all across the Empire, the first worldwide communication system, helped to unify massive areas of land. The system was retained in both the Ming dynasty and the Tsardom of Rus. The Ming and Qing both offered sacrifices to the Mongol emperors as their predecessors and continued almost all of the Mongols' multicultural religious activities, including Mongol shamanism, which helped to heal divides between ethnicities. Even the Ming founder Zhu Yuanzhang constantly spoke of himself as the rightful successor of the Yuan who restored order, not as a rebel. (David M Robinson, In the Shadow of the Mongol Empire; Robinson, Ming China and Its Allies; Robinson, the Ming Court; Jinping Wang, In the Wake of the Mongols)
Today, the Mongols (except for the neo-Nazi Khalkhas) are an important constituent nationality of the Chinese civilizational community.
We don't mind the Ming and Qing's post-Mongol label because our ancestors were honest about both the good and bad aspects of the Mongol Rule. However, in Eastern Europe people are too caught up with scapegoating Russians for everything that went wrong, which we do not need to follow.
Lithuania, Latvia and Estonia predate modern Russia.
"Modern Russia" refers here to Peter the Great's Russian Empire -
Again, same issue of self-interested perspective. According to this strand of argument, the Petrine Germanization reforms supposedly created a new Russia. The Soviet Marxist (that guy isn't Russian) reforms also created a new Russia. Mongol suzerainty, also new Russia. So, according to this logic, the Mohyla reforms which were based on Western-Jesuit ideas, spread from Kiev and became the basis of 17th century Moscow reform and the root of the modern Russian language? Did it also create a new Russia? What about the cultural influx from Byzantium to Moscow when the former collapsed, which many historians argue is the real source of Russian autocracy? also new Russia? Just a whole series of unhelpful hair splitting. Could we also say that the 1804-1819 Russian abolition of serfdom in the Baltic governorates also created a new Baltic?
refused confederation with Poland which was offered largely in good faith. Poland had always a more positive attitude toward Lithuania, while modern Lithuania is driven by aggressive insecurity and inferiority complex
I've seen so many Russians saying the exact same thing about their relationship with your country. Every strong country in the world thinks that they are doing other nations a favour by "leading" them, and every weaker country thinks that the stronger country is creating a pretext for domination, be it Colonialism, Intermarium, Warsaw Pact, NATO, East Asian Coprosperity sphere. Yes that also applies to China's foreign relations. The difference is in being able to separate feelings from logic, and analyse what this "leadership" really entails. In the USSR, it was introducing an economic system we now know to be ineffective. In the case of the US, simply suppressing all major economic competitors.