mixed bag vs accumulation

mixed bag and accumulation both are nouns.

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

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

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

mixed bag (noun)	accumulation (noun)
a collection containing a variety of sorts of things	the act of accumulating
	several things grouped together or considered as a whole
	(finance) profits that are not paid out as dividends but are added to the capital base of the corporation
	an increase by natural growth or addition