Z19851 does have certain connections with Vlachs, being found twice in Aromanian study, and interestingly not one such haplotype among Albanians but it is found in Aromanians from Albania. Generally Aromanians and Albanians seem quite different genetically, I think there might not be an SNP younger than 2000 years that they share. It's only strange that it appears among Arberesh. Also there are two E-Z19851 Bulgarians who seem only little over 1000 years distant. So bar the Arberesh, this does seem like a "Vlach clade". Actually if this clade came from Bulgaria with Vlachs, it could be actually Celtic (as simo suggested) looking at it's TMRCA and spread (N.Italy, England, Scotland..).
I think you are right about E-Z19851.
I also observed a patern that certain clades under S7461, Y16729 and J-M205 have similar distribution and are found in the British Isles, the Balkans and the Persian gulf.
What is more important is that many of those clades in the Persian gulf(f.e J-Y128487; E-BY5787) , have MRCA around 1600ybp and 1700ybp according YFULL.
That's during the height of the Roman Empire and most probably, the single factor, why those clades are in the Persian gulf.
During the reign of Trajan, 117ad, the Romans conquered Mesopotamia all the way down to the Persian gulf.
Other clades, found in the Balkans, (f.e J-Y22059, the two Bulgarians under E-Z19851), have MRCA around 1000ybp.
That's around the same time when the Vlachs first showed up in history and started migrating and assimilating into other ethnicities.
Most probably, I have MRCA with my match around the same time as shown by the calculators.
Interestingly, these clades are not found among the Albanians apart from J-M205 which is miniscule among them and most probably of Vlach origin.
That goes well with the tribal history of the Albanians and that they were 'givers' rather than receivers (assimilating others).
This can also put some light on the origins of the Vlachs and that most probably they have emerged from the retired Roman legioners and colonists in the Balkans with very different origins.
The only catalytic factor among them was the Latin language and that would explain why they never had strong national unity and were easiest to be assimilated.