low quality vs poorness

low quality and poorness both are nouns.

Word	Noun	Adjective	Verb	Adverb
low quality	Yes	No	No	No
poorness	Yes	No	No	No

As nouns, poorness is a hyponym of low quality; that is, poorness is a word with a more specific, narrower meaning than low quality:

Other hyponyms of low quality include scrawniness, scrubbiness, second class, wretchedness.

low quality (noun)	poorness (noun)
an inferior quality	the quality of being poorly made or maintained
	less than adequate
	the quality of being meager
	the state of having little or no money and few or no material possessions