simple mindedness vs simpleness

simple mindedness and simpleness both are nouns.

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

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

Other synonyms of simple mindedness include simplicity.

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