They aren’t wrong; taking the artisan out of fabrication leaves the musician as the sole artistic variable in instrument’s sonic output.
Mass produced wooden instruments still retain unique properties of the trees they were grown from. No two acoustic guitars are the same, even though they came off the assembly line within minutes of each other. Instruments made exclusively from metals and plastics aren’t as likely to have the sonic variations found in wood. This is one of the reasons cymbal companies like Zildjian offer “hand hammered” products.
edit: When I say “They’re not wrong” I don’t mean that I agree with their actions, just that the ideals they hold in regards to artisanship are not without merit. It’s great that nearly any musician can purchase a “handpan” thanks to mass production. Even a very low quality instrument can sound great in the hands of a skilled musician.