"And yes, the Magna Graecian Greeks most certainly did leave a large impact on the southern Italian genetic structure. There's no doubt about this as things stand."
Proof it.
Beginning in the 8th century BC, Greeks arrived in Italy and founded cities along the coast of southern Italy and eastern Sicily, which became known as
Magna Graecia ("Greater Greece"). The Greeks were frequently at war with the native Italic tribes, but nonetheless managed to
Hellenize and assimilate a good portion of the indigenous population located along eastern Sicily and the Southern coasts of the Italian mainland.According to
Beloch the number of Greek citizens in south Italy at its greatest extent reached only 80,000–90,000, while the local people subjected by the Greeks were between 400,000 and 600,000. By the 4th and 3rd century BC, Greek power in Italy was challenged and began to decline, and many Greeks were pushed out of peninsular Italy by the native
Oscan,
Brutti and
Lucani tribes.
I read the census book of Beloch
https://archive.org/details/diebevlkerungde00belogoog/mode/2up which looks legit. So how can a greek minority leave a "large impact" on southern italians?