Sure, Kosovo is albanian!
Also give me a few guns and some time and I will make any part of the world Russian. Serbs have been pushed out of the region, thats why they make up 10% of the population. Giving Kosovo independance is the same thing as stating that all the Baltic countries should belong to Russia due to their ethnic makeup. IIRC its what EU opposes. Why is Kosovo different?
If Hitler had done a more competent job, Russia would be German, but that hardly justifies it.
And the point is that the principle is to deal with identity and nationhood peacably, and "as is" at this moment in time.
It rules out accepting future changes through any means other than peaceful and gradual ones, and it ignores old scores as by-gones, whether some of those involved want to accept it or not. The point is also to make for as much local power of self-determination as possible, which is why it actually doesn't allow forcible empire-building. (In the EU it's the "subsidiary principle".)
The point is to break viscious historical cycles. That said, if Kosovo goes independant, we might get an isolationist Serbia at loggerheads with the EU, and determined to go to war in the future.
Otoh such a Serbia will probably be too weak to be a serious threat. While at the same time the hope is that the EU costume will eventually be able to cover and overcome these differences. In the long run, it will be kind of daft to go around picking at the scabs of local history when everyone is a EU citizen.
What's the alternative? If it's not direct Serbian repression, which the EU finds unacceptable (and everyone else), it's Kosovar self-rule, and de facto independance, except everyone will take care not to mention the dirty word, as not to hurt Serbian feelings? Things can probabaly be put in cold storage for a while like that, hoping things will resolve themselves eventually. (They often do.)
Btw, there is nowhere near a 90% Russian majority in any of the Baltic states. Parity, in one case, at best.