It depends on the codec used, I guess. I don’t know enough about Bluetooth to know if there’s any conversion that would harm the Spotify stream quality, but it’s something you should check.

I would however recommend that you get a WiiM Mini instead, which is almost as cheap and works as a full-on streamer, with a toslink out that you can connect to the DAC

No. Its cartridge isn’t replaceable.

My subjective opinion: music that was originally intended for vinyl sounds better on vinyl, music that was originally intented for digital sounds better on digital. That trumps any technical consideration that might arise about the formats themselves.

In the end, I think this discussion is moot. People might say they want the highest fidelity possible, but how many of them are choosing completely neutral, monitor-like setups? They almost always look for warmth somewhere, for brightness somewhere else… those are distortions just as much.