Comment by jordigh

I generally distrust modern Greeks' knowledge about Ancient Greek. For example, beta has changed pronunciation, becoming something like English v instead of English b like it was originally, but most modern Greeks will vehemently deny that the pronunciation has changed.

We have good evidence that it used to be like English b (voiced bilabial plosive):

https://www.foundalis.com/lan/betapro.htm

That's just one example. Native speakers are usually the worst at understanding and explaining their own language.