poor speller vs writer

poor speller and writer both are nouns.

Word	Noun	Adjective	Verb	Adverb
poor speller	Yes	No	No	No
writer	Yes	No	No	No

As nouns, writer is a hypernym of poor speller; that is, writer is a word with a broader meaning than poor speller:

poor speller (noun)	writer (noun)
someone who spells words	writes (books or stories or articles or the like) professionally (for pay)
	a person who is able to write and has written something