of the essence vs all-important

of the essence and all-important both are adjectives.

Word	Noun	Adjective	Verb	Adverb
of the essence	No	Yes	No	No
all-important	No	Yes	No	No

As adjectives, of the essence and all-important are synonyms defined as:

Other synonyms of of the essence include all important, crucial, essential.

of the essence (adjective)	all-important (adjective)
of the greatest importance	of the greatest importance