ping.
1.)The Romans conquer Britannia and Mediterranean genes are introduced.
2.) Centuries pass. The Roman Empire collapses and Britannia is invaded by multiple waves of Germanic and Scandinavian invaders.
3.) The surviving Romano-Britons are pushed out of the indefensible lowlands but are able to mount a successful defense in the mountainous regions of Wales just as the Asturians mounted a successful defense against the invading Moors in their mountainous region of northwest Spain.
4.) Mediterranean genes survive in Wales and are concentrated in Wales.
They are burdened by "the English filter" ~ a well known phenomenon where any idea not already accepted by English speakers is simply rejected out of hand and a new answer sought.
I suppose that stimulates more study, but it overlooks a lot of things already known from sources the Brits don't wish to study.
With respect to Eastern Mediterranean sources for y-chromosome purposes it doesn't matter if that didn't happen 4,000 years ago since, in fact, it did happen about 2500 (average) years ago.
The otherwise discredited sources are the Galician version of the Annals of the Kings. This is yet another version of history that was maintained by Gaelic speakers in Northern Spain BEFORE the Milesians invaded Ireland.
The next step in that invasion was when the Irish moved to Great Britain. That happened before the arrival of the Romans.
The Romans were in the habit of bringing foederati to conquered lands ~ so you could have some Eastern Mediterranean types brought to Great Britain at that time ~ remember, it only takes ONE GUY to pull this off.
quoting further:
"This type of genetic make-up is usually found in the eastern Mediterranean which made us think that there might have been strong connections between north-east Wales and this part of Europe somewhere in the past.But this appears not to be the case, so we're still looking to find out why it's happened and what it reveals about the history of the region."
The article gives no explanation for why their original assumptions of 4,000 year old, Bronze Age -- think Stone Henge -- connections are now rejected.
Careful DNA analysis might suggest when those connections were first made, and this in turn provide the beginnings of understanding.
I would suggest that, without some solid evidence to the contrary, researchers should not automatically rule out Bronze Age.
There was more going on in those times than we really understand today.