The main reason vinyl often sounds better is because it is better mastered, so this is concerning.

That's just not true and vinyl doesn't sound better by any measure.

It's true from time to time. Low's last digital releases are actually unlistenable due to heavy-handed compression, but the vinyl seems to have been spared.

I had to record the vinyl to get usable digital files.

The loudness and compression on Low's last couple of albums is very much deliberate, so it's surprising that the vinyl doesn't have it. Though I heard similar claims about Sleater-Kinney's The Woods, which was also intensely compressed for artistic effect.

This. The loudness is an aesthetic choice.

The reason it was backed off for the vinyl master is most likely due to physical limitations of the medium. If the audio channels are too loud (wide) there is risk that the needle will jump out of the groove.

There's compression and distortion for sure on the vinyl, but when you look at the waveform on the digital it's right up to the max. It completely changes the sound.

It’s completely true, when the vinyl has a different mastering. It can be a completely different version. It’s not because it’s vinyl

I'd say "rarely" instead of "often" though it depends on the genre I guess. There are also a lot of genres that can never sound as good on vinyl simply due to the lack of dynamic range/silence; mostly classical and electronic.