That was true 10 years ago but not today. Schott glass (Zeiss and IOR Valdada) is still some of the best glass in the world. The glass coming out of Hungry (Schmidt & Bender) is considered just as good as is the glass coming out of Austria (
Kahles and Swarovski). Quality glass or fluorite with precision surface grinding resulting in few aberrations, very good edge to edge sharpness, excellent resolving power and quality coatings have been and still are their hallmarks. These days the Japanese are the equal or in some cases better however. The fluorite lenses in the current line of Kowa scopes bests those of the finest European brands in all reviews. I've looked though Zeiss, Leica and Kowa. The Kowa's are difficult to beat. The Japanese make the glass used in Nightforce, some Leica products and the higher end Leupold, Nikon, Sightron and Vortex scopes. The Korean's make the glass for the scopes in the next lower price range and some of it is very good. The Chinese make the glass for the cheapest scopes. The US does not really make optical glass. Rumor has it that Corning was making some Leica glass but that is difficult to ferret out.
Yes, I'm a glass snob.