They’re not at all the same people. We don’t really have strong evidence of writing from the Nuragic civilisation, but the Etruscans left plenty of written evidence and their language was probably not even Indo European. Then there were invasions by the Gauls and the Latins, who built the Roman Empire, but they were taken over by Germanic peoples, who partially integrated. Waves and waves of people speaking different languages, with different religions and customs.

You say that modern English have always been there, but again, after the Celts got taken over by the Romans, there was a long period of Roman rule, with a lot of cultural and ethnic mixing. Then came the Saxons, again a people with completely different language and customs. This was a large mixing of populations and a huge shift in culture. Then there was an invasion of Vikings that was so significant that a huge part of east England was called the Danelaw, because it was under Danish control. You still see that in place names and surnames. Then in 1066 the Norman French came, again massively changing the culture, the language and the political structures.

It’s the same story all over Europe. Wave after wave of invasion, displacement and cultural shift and mixing.