affection vs soft spot

affection and soft spot both are nouns.

Word	Noun	Adjective	Verb	Adverb
affection	Yes	No	No	No
soft spot	Yes	No	No	No

As nouns, soft spot is a hyponym of affection; that is, soft spot is a word with a more specific, narrower meaning than affection:

Other hyponyms of affection include attachment, fond regard, protectiveness, regard, respect.

affection (noun)	soft spot (noun)
a positive feeling of liking	a place of especial vulnerability
	any membranous gap between the bones of the cranium in an infant or fetus
	a sentimental affection