>They just conquered 10% of Ukraine, so they might do that 10 more times.

How? Meatgrind the rest of the country? That's going to cause immense losses among Russian troops and sowing as much discord as possible in Russian civil society seems like a great strategy to prevent that.

>They want a stable Russia

They want a Russia that is economically advantageous to them. Too much Russian success will cause Europe to become even more reliant on the US and therefore antagonistic to China. China's and Russia's interests are not aligned.

>They walked in, were surprised by unexpected resistance, walked out and resorted to taking back the parts of Ukraine that prefer to speak Russian.

This is cope. Look at how much it took to take Bakhmut.