Back to the topic, I would personally attribute the higher "Slavic" admixture to the Vlachs in both Greece and Albania. It's not far fetched to think that Thracians had more NE admixture than Illyrians and Greeks.
A lot of that nonsense was propagated by Arvanites themselves to be fair (see Kollias and his attempt to connect Arvanitika to Homeric Greek, we both posted in a thread where an Albanian user posted that theory in fact) because they wanted a linguistic connection to ancient Greece that just wasn't there.
Y-DNA wise the Aromanians seemed to differ quite a bit from place to place but I've never come across autosomal results, it's a topic I haven't looked into, to see what they look like from place to place so you might be right. Much of the 'Slavic' admixture must be genuinely Slavic though considering the toponymy in both Albania and Greece.
Also we have a 5th century Thracian genome from Bulgaria now (in the Mathieson et al. paper about Southeastern Europe) and she didn't look particularly 'northeastern', she seemed to be very heavily Neolithic in fact (not unlike those Mycenaeans with high Neolithic and low steppe - but with probably no/less extra CHG-Iran stuff in her case), but we'll probably be able to tell better when the genomes are released and we definitely need better temporal and spatial coverage for a clear picture. That Mathieson paper showed individuals from the same location could differ quite a bit in their ancestral proportions after all but perhaps by the 5th century it was already starting to homogenize.
For the time being it does seem like something might have increased the average steppe ancestry and depressed the Neolithic one in the Balkans in post-Classical times (and it might be instructive that Albanians -especially- and Greeks are somewhat more Neolithic and somewhat less steppe than the Slavic-speaking Balkan peoples but like you said, variation might have already existed, and it isn't like Albanians and Greeks must have remained untouched by anything else either) but we'll see.
I don't blame Angela btw, you know what shitshows we can turn those Balkan threads into, we've seen it here too.