simpleness vs simple mindedness

simpleness and simple mindedness both are nouns.

Word	Noun	Adjective	Verb	Adverb
simpleness	Yes	No	No	No
simple mindedness	Yes	No	No	No

As nouns, simpleness and simple mindedness are synonyms defined as:

Other synonyms of simpleness include simplicity.

simpleness (noun)	simple mindedness (noun)
the quality of being simple or uncompounded	a lack of penetration or subtlety
lack of ornamentation
freedom from difficulty or hardship or effort
a lack of penetration or subtlety