Surely, that’s the crux of it, it’s a preference/opinion, yours included. There was another thread where the thumb position was part of the argument and there were plenty of photos of the great and the good wrapping their thumbs over the top. If a slim or narrow neck helps folk to play better, the way they prefer to play, then it’s all good, as it’s surely the music that is produced that is important. The same applies to the skinny stringed thing. Modern electric bass and electric guitar are certainly an evolved versions of the DB and classical guitar, but technique evolves too, although it’s not necessarily a prerequisite. Telling people they should just go and practise could be regarded as somewhat arrogant and not considerate of other’s needs or physicality. If you think skinny/fast necks are a marketing ploy, you’re entitled to that opinion and you don’t have to use them, but don’t be surprised if others disagree and keep buying slim, skinny necks (FWIW, I prefer a bigger handful, but that’s me).