E-L241 is a good example, because there is one major Albanian founder branch (
E-PH2180), some branches in which Albanians participate (like E-Z38770), but in no way dominant and it could easily go the other way around (into Albanians later, after the ethnogenesis) and then there is a clearly Serbian branch (E-Y178925).
Outside of Kosovo most Serbs under E-L241 are from the Serbian or other not clearly Albanian branches. What kind of E-L241 dominates in Kosovo Serbs - who knows? I'm genuinely asking for evidence regardless of where it leads to.
Haplogroups like E-Z1057 or E-Z5018 mean nothing, they are to general.
Another aspect is the testing frequency: How important are Sardinians for E-V13? They don't even represent the source in Italy, with their ancestors coming mainly from North Western Italy, especially Genua-Liguria. The main reason Sardinians are so overrepresented, is, that they are better tested due to this one big study.
Similarly, not every branch in which a single Albanian pops up has to be "an Albanian branch". There are clear founder branches of Albanians, like
E-FGC33646,
E-Y173822 or
E-Y146090 etc. There are really many of such Albanian founder branches. But not every single sample makes a branch as a whole Albanian derived. Or do the single Sardinian sample make all the branches Sardinian derived? I don't say so.
There are always two ways to claim a branch for a specific ethnicity in my book:
1) Ancient DNA finds - that's straightforward
2) Founder events in a specific time frame, with a clearly documented branching event within an ethnicity, deduced from modern DNA samples.
A single sample doesn't prove an ethnic affiliation. Even many samples don't prove an ethnic affiliation with certainty, if they don't within in a short period of time. Like my own branch has now many ethnic Germans, but we are all pretty distant to each other, so I can't claim having any evidence for a deep German/Germanic origin for my branch.
The same applies to the well-tested Albanians. Single samples only prove the possibility of an Albanian or better Pre-Albanian affiliation, but they don't make it an Albanian branch. The migration or gene flow could have gone the other way too.