I don't know if that is true. Stuff just changes. To solve similar problems to this, my lab developed sapphire metal bonding techniques that could be run with CNC machined parts. Everything became nice and reliable and repeatable.

We lose techniques all the time but gain new ones. I designed a scientific instrument once that had a long precision bore through it. I designed it with the belief that I needed clearances for a large stiff boring bar to make the feature.

I showed the prints to my machinist, and he told me they were just gonna put it on the five axis and hit the bore on both sides with an end mill. That it was as accurate as how the old guys did it.

It was.