bottom dog vs foot soldier

bottom dog and foot soldier both are nouns.

Word	Noun	Adjective	Verb	Adverb
bottom dog	Yes	No	No	No
foot soldier	Yes	No	No	No

As nouns, foot soldier is a hypernym of bottom dog; that is, foot soldier is a word with a broader meaning than bottom dog:

Other hypernyms of bottom dog include subordinate, subsidiary, underling.

bottom dog (noun)	foot soldier (noun)
a person of low status	fights on foot with small arms
	an assistant subject to the authority or control of another