1. It's difficult to explain to an outsider but there's a racist slur in Serbia and FYROM according to which Bulgarians are Mongols or Tartars which the Serbs connect with uncleanliness and barbarity. I myself have no problems with any of that (besides language groups and races are completely different things, but how would you explain that to crazy nationalists). Notice how Danubian Cossack immediately involved Tartars in Russia which is completely removed from the subject...
2. Still none of that has any connection with Macedonia in the late Middle Ages which is the subject of the thread.
1. This is disgustingly racially charged and a despicable attitude to hold. There is nothing admirable or defensible about using people from central Asia as the butt of an insult, and it is offensive to then say that you are upset that someone might insinuate you are of a certain heritage. Your statement is, basically, tantamount to saying Slavic > Turkic because calling someone Turkic/Mongol is an insult. In my country, the racial term is applied to people of African descent, and someone being upset at an insinuation that they descended from an African ancestor (eg every human) because it relates them to said negative-term stereotyped race, is in the wrong.
In other words, if you believe that being of a certain racial descent is an insult or inferior to being of a different racial descent, you are the one in the wrong.
2. DC's entire post was to point out that the cultural identity of the region in the 1444 start would have been of a Slavic background, which he terms Serbian for the game's limiting structure, and would not have been of a central Asian ethnicity - Bulgarian (at this time), Turkish, Hungarian, etc. They seemed like fair and very valid points.
That doesn't change anything. The games represents the ruling classes in a province not the majority of the population since those were the people mentioned in documents and censuses. Take for example Transylvania, peasants were Romanians but the rulers were Hungarian, in-game it's Hungarian. Or take Cornwall, or Languedoc
This is only done in arbitrary cases for specific reasons. On the whole, the game attempts to model what the majority of the residents of an area's culture would be. Some cases are simplified, eg the British isles, said to be for balance reasons. Some like the low countries for gameplay and historical direction reasons. Some like the Baltics or Cyprus are left as realistic as the devs feel possible.
In the case of the southern Balkans and western Anatolia, we've seen culture and religion flip, so clearly they adjust based on both their knowledge/understanding of the region's cultural and religious history, but also for balance reasons. In this case, I think if someone could make a compelling and definitive case for the culture to be specifically X culture, they would probably go ahead and make the province fit that.