There's no direct continuation from ancient Greeks to moderns like in the heads of some posters here (not you obviously).
There is no group that jumps over 5000 year of linguistic, military, and imperialist expansion like the Greeks (and then the Romans) and remains as such in 2023.
The uniparentals are proof of this, on top all of the medieval literature and accords that we have. Within 10 generations the autosomals are wiped out, only the original uniparental markers remain and these confirm the literature, with the amount of E-V13 (Dacians) and Ia2-din (Bulgarians/South-Slavs) you see in peninsular Greece (don't take my word for it, just visit the FTDNA project and check for yourself). The reason that 'mainland' Greeks are not absolutely identical to Albanians and Bulgarians/North-Macedonians is because they have received Anatolian and Armenia-BA (loose usage of the term) input that pulls them south, exactly what the historical sources tell us. They were Byzantines/Greeks and subject to such admixture input.
The similarity of a PCA is just that, a similarity that applies to various groups of the region of the Eastern Mediterranean, and for a good reason. If we take the PCA argument to its logical extreme, the Ashkenazi Jewish people are actually equal candidates for ancient Greek ancestral origin, yet no one argues such a point.
As for the Greek people who push for such unbroken continuities and notions of genetic purity, they are sick in the head, they might not be nordicists but they are the Med equivalent.
If anyone wants to read for themselves what transpired in this part of the world in terms of migrations and population dynamics between 330 A.D. (the creation of Constantinople (the point of origin that most scholars consider the birth of the Greco-Roman syncretic ethnos)) till about 1836 (the creation of the Kingdom of Greece and the Romantic revival of the ancient classics as the new identity of the Rumelian Romans/Rhomaioi) then I can PM relevant literature, I feel like a broken record.
Here are the percentages of different Y-DNA Haplogroups by country:
https://www.eupedia.com/europe/european_y-dna_haplogroups.shtml
[TABLE="width: 1218"]
[TR]
[TD="class: xl63, width: 87"][TABLE="width: 1305"]
[TR]
[TD="class: xl65, width: 87"]Region/Haplogroup[/TD]
[TD="class: xl82, width: 87, align: right"]I1[/TD]
[TD="class: xl83, width: 87, align: right"]I2*/I2a[/TD]
[TD="class: xl84, width: 87, align: right"]I2b[/TD]
[TD="class: xl85, width: 87, align: right"]R1a[/TD]
[TD="class: xl86, width: 87, align: right"]R1b[/TD]
[TD="class: xl87, width: 87, align: right"]G[/TD]
[TD="class: xl88, width: 87, align: right"]J2[/TD]
[TD="class: xl89, width: 87, align: right"]J*/J1[/TD]
[TD="class: xl90, width: 87, align: right"]E1b1b[/TD]
[TD="class: xl91, width: 87, align: right"]T[/TD]
[TD="class: xl92, width: 87, align: right"]Q[/TD]
[TD="width: 87, align: left"]
[/TD]
[TD="class: xl81, colspan: 2"]Sample size ▾[/TD]
[/TR]
[TR]
[TD="class: xl65"]Greece[/TD]
[TD="class: xl66, align: right"]3.5[/TD]
[TD="class: xl67, align: right"]9.5[/TD]
[TD="class: xl68, align: right"]1.5[/TD]
[TD="class: xl69, align: right"]11.5[/TD]
[TD="class: xl70, align: right"]15.5[/TD]
[TD="class: xl71, align: right"]6.5[/TD]
[TD="class: xl72, align: right"]23[/TD]
[TD="class: xl73, align: right"]3[/TD]
[TD="class: xl74, align: right"]21[/TD]
[TD="class: xl75, align: right"]4.5[/TD]
[TD="class: xl76, align: right"]0[/TD]
[TD="class: xl77, align: right"]0[/TD]
[TD="class: xl78"][/TD]
[TD][/TD]
[/TR]
[TR]
[TD="class: xl79"]North Greece[/TD]
[TD="class: xl66, align: right"]5.5[/TD]
[TD="class: xl67, align: right"]16[/TD]
[TD="class: xl68, align: right"]1[/TD]
[TD="class: xl69, align: right"]18[/TD]
[TD="class: xl70, align: right"]13[/TD]
[TD="class: xl71, align: right"]4.5[/TD]
[TD="class: xl72, align: right"]15[/TD]
[TD="class: xl73, align: right"]2.5[/TD]
[TD="class: xl74, align: right"]20.5[/TD]
[TD="class: xl80, align: right"]4[/TD]
[TD="class: xl76, align: right"]0[/TD]
[TD="align: left"]
[TD="align: left"]
[/TD]
[TD="align: left"]
[/TD]
[TD="class: xl77, align: right"]0[/TD]
[/TD]
[TD="class: xl78"][/TD]
[TD][/TD]
[/TR]
[TR]
[TD="class: xl79"]Central Greece[/TD]
[TD="class: xl66, align: right"]3.5[/TD]
[TD="class: xl67, align: right"]7[/TD]
[TD="class: xl68, align: right"]3.5[/TD]
[TD="class: xl69, align: right"]11[/TD]
[TD="class: xl70, align: right"]11.5[/TD]
[TD="class: xl71, align: right"]6[/TD]
[TD="class: xl72, align: right"]19[/TD]
[TD="class: xl73, align: right"]3.5[/TD]
[TD="class: xl74, align: right"]29.5[/TD]
[TD="class: xl80, align: right"]5[/TD]
[TD="class: xl76, align: right"]0[/TD]
[TD="class: xl77, align: right"]0[/TD]
[TD="class: xl78"][/TD]
[TD][/TD]
[/TR]
[TR]
[TD="class: xl79"]South Greece[/TD]
[TD="class: xl66, align: right"]1.5[/TD]
[TD="class: xl67, align: right"]9[/TD]
[TD="class: xl68, align: right"]1[/TD]
[TD="class: xl69, align: right"]10.5[/TD]
[TD="class: xl70, align: right"]20.5[/TD]
[TD="class: xl71, align: right"]3.5[/TD]
[TD="class: xl72, align: right"]19.5[/TD]
[TD="class: xl73, align: right"]1[/TD]
[TD="class: xl74, align: right"]27[/TD]
[TD="class: xl80, align: right"]4.5[/TD]
[TD="class: xl76, align: right"]0[/TD]
[TD="align: left"]
[TD="align: left"]
[/TD]
[TD="align: left"]
[/TD]
[TD="class: xl77, align: right"]0[/TD]
[/TD]
[TD="class: xl78"][/TD]
[TD][/TD]
[/TR]
[TR]
[TD="class: xl79"]Crete[/TD]
[TD="class: xl66, align: right"]4[/TD]
[TD="class: xl67, align: right"]7[/TD]
[TD="class: xl68, align: right"]1[/TD]
[TD="class: xl69, align: right"]9[/TD]
[TD="class: xl70, align: right"]15[/TD]
[TD="class: xl71, align: right"]9.5[/TD]
[TD="class: xl72, align: right"]34[/TD]
[TD="class: xl73, align: right"]5[/TD]
[TD="class: xl74, align: right"]11[/TD]
[TD="class: xl80, align: right"]4[/TD]
[TD="class: xl76, align: right"]0.5[/TD]
[TD="class: xl77, align: right"]0[/TD]
[TD="class: xl78"][/TD]
[TD][/TD]
[/TR]
[TR]
[TD="class: xl79"]Aegean Islands[/TD]
[TD="class: xl66, align: right"]3[/TD]
[TD="class: xl67, align: right"]3[/TD]
[TD="class: xl68, align: right"]2.5[/TD]
[TD="class: xl69, align: right"]10[/TD]
[TD="class: xl70, align: right"]19[/TD]
[TD="class: xl71, align: right"]8.5[/TD]
[TD="class: xl72, align: right"]20[/TD]
[TD="class: xl73, align: right"]3[/TD]
[TD="class: xl74, align: right"]22[/TD]
[TD="class: xl80, align: right"]6[/TD]
[TD="class: xl76, align: right"]0[/TD]
[TD="align: left"]
[TD="class: xl77, align: right"]0[/TD]
[/TD]
[TD="class: xl78"][/TD]
[TD][/TD]
[/TR]
[/TABLE]
[/TD]
[TD="class: xl79"][/TD]
[TD="class: xl80, width: 87"][/TD]
[TD="class: xl81, width: 87"][/TD]
[TD="class: xl82, width: 87"][/TD]
[TD="class: xl83, width: 87"][/TD]
[TD="class: xl84, width: 87"][/TD]
[TD="class: xl85, width: 87"][/TD]
[TD="class: xl86, width: 87"][/TD]
[TD="class: xl87, width: 87"][/TD]
[TD="class: xl88, width: 87"][/TD]
[TD="class: xl89, width: 87"][/TD]
[TD="width: 87, align: left"][/TD]
[TD="class: xl91, width: 87"][/TD]
[/TR]
[/TABLE]
There is no objections to the slavic input we all acknowledge that. EV-13 on the other hand there is a lot of discussion as to its provenance. Let's wait until we have a lot more samples throughout the balkans and throughout history before we jump to conclusions.