elite group vs upper crust

elite group and upper crust both are nouns.

Word	Noun	Adjective	Verb	Adverb
elite group	Yes	No	No	No
upper crust	Yes	No	No	No

As nouns, upper crust is a hypernym of elite group; that is, upper crust is a word with a broader meaning than elite group:

elite group: a group or class of persons enjoying superior intellectual or social or economic status
upper crust: the class occupying the highest position in the social hierarchy

Other hypernyms of elite group include upper class.

elite group (noun)	upper crust (noun)
a group or class of persons enjoying superior intellectual or social or economic status	the class occupying the highest position in the social hierarchy