There is also the phrase 'never look a gift horse in the mouth'. And never mind schools of thought. There are lots of real schools that can't afford instruments at all. The last thing any teacher should be doing is turning their nose up at an instrument given by anyone who cares about the instrument in principle, and made an effort to set it up properly. If people don't make the best of what they have, or can get at need, or by luck, do they warrant getting anything better?
I understand that a working bike beats a box of bits to learn from, and it should be acceptable as a basic standard, and by the same logic the origin and price of an instrument should not automatically exclude it. I remember when all the descant recorders were cheap and made of plastic in primary school, they worked well enough to learn from.
I originally rejected the Westone Thunder 1-A bass as a consideration because it was made in Japan and sold in Britain via mail order catalogs that were very easy to be snobbish about. I assumed I could easily do better. Fortunately it didn't take me long to rethink that thought and get a used one when a Status Graphite wasn't getting me what I wanted from it. There will always be 'better' instruments, but if I'd learned on the Westone instead of my first Status Graphite, I'd be better at playing them than I am now. It turns out that the Westones are very good basses, not just 'good for the money'. Less easy to play than the Status, but more rewarding of the effort.
It was a sub...