I live near the Glock plant in Georgia and know someone who works there. While he’s probably biased to a degree, he said there is no difference from a production line perspective to manufacturing here vs Austria. He also said they send parts for some models to Europe from Smyrna, and vice versa.
This is a similar topic to Sig, where some people swear that German made Sigs are somehow “better” than those made in NH. Not sure how a stamped sheet metal slide is better than one milled out of a stainless steel blank, but that discussion continues.