I think Serbs need one sample of minimum 500 samples, combining is not good. I believe Thrachians are E-V13,J2b2 and R1b-HT 35. I think both R1a and I2a in Balkan are mostly connected with Slavs, both groups are big in Balkan Slavs but not in Albanians and Greeks. The difference in the Balkan Slavs and Albanian/Greeks is the amount of R1b-HT35/J2b2,J1 and R1a-M458,R1a-Z280,I2a-Din . E-V13 is big in everybody
As for the second assumption maybe 17th-18th century, some Orthodox Albanians have become Bulgarians/Macedonians and Serbs/Montenegrins and a lot have become Greeks, some Muslim Bulgarians and Serbs have become Albanians is my theory. Religion was really strong thing, a lot of Torbesh in FYROM have become Albanians lately 18th-19th century).
Internet theories that J2 in Albos is from Turks are one big joke, coz J2b2 is a Balkan group and J-M530 and J-M67 are Med/West Asian groups which are in Europe from before the time of Jesus.
Yes, internet theories are frivolous, and we do not take in account. However your assumption about assimilation is very interesting.
I always thought Thracians as dominantly E1b1b1a1 people (with mix another haplogroups), but here in forum there is big group who argue that Thracians are dominantly I2a2+R1a.
Movements of R1a are interesting, because carriers of R1a according to science came three times in Balkans and only last time refers to the expansion of Slavs. Regueiro et al. (2012), Klyosov (2009) and another scientists claim that R1a is the oldest haplogroup in the Balkans (of the existing).
I started thread about haplogroup of people who developed the culture at Lepen Whirl, east Serbia, 7 millennia ago. Researches of people in past would give a more realistic picture, we still here talking about assumptions, less about facts, essential tool (based on facts) are results of haplogroups.
We know now that R1a in Balkans in good part is not connected to Slavs. One of key questions is whether I2a2 is connected to Slavs, wholly or mainly on the one hand, or less (or not at all) on the other hand.
My opinion is that clarification of Thracian Y-DNA will lead to a clearer picture.
You write that events of the last few hundred years changed the situation. They could (ethnic cleasing, immigrations/emigrations). But assimilation don't change haplogroups, carriers of haplogroups remain, just in the case of assimilation they can be part of another nation (and religion). Your assumption about assimilation in related to my question is valuable.