red herring vs diversion

red herring and diversion both are nouns.

Word	Noun	Adjective	Verb	Adverb
red herring	Yes	No	No	No
diversion	Yes	No	No	No

As nouns, diversion is a hypernym of red herring; that is, diversion is a word with a broader meaning than red herring:

red herring: any diversion intended to distract attention from the main issue
diversion: a turning aside (of your course or attention or concern)

Other hypernyms of red herring include deflection, deflexion, deviation, digression, divagation.

red herring (noun)	diversion (noun)
any diversion intended to distract attention from the main issue	an activity that diverts or amuses or stimulates
a first draft of a prospectus; must be clearly marked to indicate that parts may be changed in the final prospectus	a turning aside (of your course or attention or concern)
a dried and smoked herring having a reddish color	an attack calculated to draw enemy defense away from the point of the principal attack