It didn't "confirm" what we "already knew", unless by "we" you mean mattoids from anthrogenica and other delusional individuals.
I have grown accustomed to cr*p being published but I shan't pretend it is good scholarship. If you think that I am too harsh go take a look at their qpAdm models: Cretans, who are mostly similar to south Peloponnesians, are modelled as having literally more ancestry from Ottoman Turks than ancient Greek ancestry which is literally zero (even if we are to take the "western anatolian" as a mix of Greeks and older Anatolian_BA-like Anatolians it would still make a 35% contribution from western Anatolia and oddly enough such a profile would have spread quite uniformly all over the Balkans). and the 20% Slavic is quite ridiculous.
What is most laughworthy though is that by PCA position AND distal ancestry proxy modelling (so I don't take PCA at face values as the only basis of my skepticism) southern Europeans are mostly similar to their respective ancestors, with Cretans and southern Peloponnesians being literally a hair above ancient Greek samples on the PCA- exactly as you'd expect if those populations have negligible Slavic input-, to take an example, but such similarities/affinities are owed to very coincidental and fortuitous mixing of both "southern" and "northern" sources. Of course such models aren't then checked out against haplogroups, f4/f3 stats, etc...
It is the same idiocy I saw with the Etruscan paper or the upcoming paper from north Italy according to which north Italians "happen" to be similar from Italics from north Italy thanks to a very fortuitous mixing of both "southern" and "northern" sources- which turns out to be 20% "east med", however it is defined, 20% Germanic and the remaining 60% Italic, so literally equal amounts of both which very conveniently "cancel each other out".
I have also many suspicions about the representativity of the Dodecanese samples, since in older papers they were basically identical to Cretans,
https://www.pnas.org/doi/10.1073/pnas.1320811111 ,
https://onlinelibrary.wiley.com/doi/full/10.1111/ahg.12328 , and on top of that the paper on Peloponnesians, this
https://www.nature.com/articles/ejhg201718 , has western anatolian Greeks mostly similar to Peloponnesian ones, so I wonder whether these Dodecanesian samples are from descendents of more recent arrivals whose genetic profile is being taken as representative of the whole dodecanese and projected very back in time- and it does seem to me there's too much heterogeneity for samples from a tiny island if they are all from locals whose ancestry dates back to the hellenistic period without significant further contributions.