first-rater vs doer

first-rater and doer both are nouns.

Word	Noun	Adjective	Verb	Adverb
first-rater	Yes	No	No	No
doer	Yes	No	No	No

As nouns, doer is a hypernym of first-rater; that is, doer is a word with a broader meaning than first-rater:

Other hypernyms of first-rater include actor, worker.

first-rater (noun)	doer (noun)
one who is first-rate	a person who acts and gets things done