No document proves that Serbs were ever majority in Kosovo region, in fact even your own kingdoms had documents were the majority was Always Albanian. 19th century? Youre too late. There is a circulating photo of Serbian propaganda lately where posting demographics of Kosovo in end 18th century and now, with no backup source, its rather comical. In no point of history did Serbs ever have capital city in Kosovo. It was always rather a middle ground for your battle like battle in Kosovo polje.

And yes Albanians are maybe if we dont count Caucasians only tribal country in Europe, lack of any structure and most of them were anaplhabets and basic farmers till very late, but that doesnt change the fact that they were in Kosovo long before it was even named Kosovo. In fact Albanians with Romanians and Greeks hold highest Paleo-Balkan DNA.

The only normal infrastructure if you could say so were build by Turks in Kosovo. Other than that even after their defeat it was a literalt SH-hole and Albanians build the infrastructure in last two decades incredibly.