> I bought myself for just a few euro a Bluetooth DAC (a FiiO) that had superior sound quality to any phone’s audio-out that I had ever used.

I hate the 3.5'' jack myself (see below), but I can already tell you that mentioning some unscientific definition of "superior sound quality" that likely no one amongst us is humanly able to distinguish is not going to win any minds over. Proponents of 3.5'' like it because it is ridiculously simple to use, intuitive, cheap, doesn't have a lot of things that can go wrong (e.g. no batteries) and despite that is overall effective.

The reason I dislike 3.5'' is because the _socket_ part (i.e. the part on the expensive device) wears out very quickly, becoming fragile and generating distracting artifacts even with slight cable pulls/movements, as the springs in the connector start to fail. This annoys me to no end, much more than any issues with other interfaces.