Right. I occasionally hear local word-rich rap and it is low quality lyrics overall. In particular, it’s like they explain every line with ten more lines, as if their listener was an idiot who cannot read between these.

If I looked for a good metric, I would probably take min(word per meaning and touch), but that would raise a question on what ‘meaning and touch’ is. Nonetheless, good lyrics always seem to be un/under-spoken or sharp cut.

Yes! In poetry, William Carlos Williams is a great example. In music, Lou Reed and Randy Newman are good examples.

Ok fine, objectively there's less lyric content and more repetition; and subjectively the lyrics aren't exactly getting more insightful or laconic to compensate.

I'd say that writing in music tends to be pretty terrible across the board - with a few exceptions during each period.