substitutability vs substitutable

substitutability is a noun but substitutable is not a noun.

Word	Noun	Adjective	Verb	Adverb
substitutability	Yes	No	No	No
substitutable	No	Yes	No	No

substitutability (noun)	substitutable (noun)
exchangeability by virtue of being replaceable

substitutability (adjective)	substitutable (adjective)
	capable of being exchanged for another or for something else that is equivalent
	(of words) interchangeable in a given context without changing the import of the expression