mixed bag vs collection

mixed bag and collection both are nouns.

Word	Noun	Adjective	Verb	Adverb
mixed bag	Yes	No	No	No
collection	Yes	No	No	No

As nouns, collection is a hypernym of mixed bag; that is, collection is a word with a broader meaning than mixed bag:

Other hypernyms of mixed bag include accumulation, aggregation, assemblage.

mixed bag (noun)	collection (noun)
a collection containing a variety of sorts of things	the act of gathering something together
	a publication containing a variety of works
	request for a sum of money
	several things grouped together or considered as a whole