I think the assumption that a producer of audio gear would supply the best possible tubes is not realistic. They need tubes that are both reliable and can be acquired in large quantities. Most audiophiles who own tube gear eventually find the sound can be improved and modified to their taste with aftermarket tubes. I've done this with virtually every piece of tube gear I've owned. In fact the only gear I ever bought that didn't come stock with current production tubes were my Quicksilver Monoblock power amps. That's because they are a small production company and they bought up a large quantity of 1970s vintage Tesla tubes for their gear.
If you will excuse the analogy, buying tube gear is a bit like buying a bicycle. The seat it comes with usually is usually very basic and not that comfortable. So you buy a new seat to suit your butt so you can have more comfort performance. Same with tubes