waste of time vs wastefulness

waste of time and wastefulness both are nouns.

Word	Noun	Adjective	Verb	Adverb
waste of time	Yes	No	No	No
wastefulness	Yes	No	No	No

As nouns, wastefulness is a hypernym of waste of time; that is, wastefulness is a word with a broader meaning than waste of time:

waste of time: the devotion of time to a useless activity
wastefulness: useless or profitless activity; using or expending or consuming thoughtlessly or carelessly

Other hypernyms of waste of time include dissipation, waste.

waste of time (noun)	wastefulness (noun)
the devotion of time to a useless activity	useless or profitless activity; using or expending or consuming thoughtlessly or carelessly
	the trait of wasting resources