drop-off vs falling off

drop-off and falling off both are nouns.

Word	Noun	Adjective	Verb	Adverb
drop-off	Yes	No	No	No
falling off	Yes	No	No	No

As nouns, drop-off and falling off are synonyms defined as:

drop-off and falling off: a noticeable deterioration in performance or quality

Other synonyms of drop-off include falloff, slack, slump.

drop-off (noun)	falling off (noun)
a change downward	a noticeable deterioration in performance or quality
a steep high face of rock
a noticeable deterioration in performance or quality