drop like flies vs break down

drop like flies and break down both are verbs.

Word	Noun	Adjective	Verb	Adverb
drop like flies	No	No	Yes	No
break down	No	No	Yes	No

As verbs, break down is a hypernym of drop like flies; that is, break down is a word with a broader meaning than drop like flies:

Other hypernyms of drop like flies include collapse.

drop like flies (verb)	break down (verb)
rapidly collapse, die, or drop out in large numbers	collapse due to fatigue, an illness, or a sudden attack
	stop operating or functioning
	separate (substances) into constituent elements or parts
	make a mathematical, chemical, or grammatical analysis of; break down into components or essential features
	make ineffective
	cause to fall or collapse
	lose control of one's emotions
	fall apart