Learn English – What adjective or phrase can describe that there is a lot of information

Underrated might be what you're looking for. It means something that deserves more attention than is given to it.

The question begins:

Hyphenating an adjective composed of two words is, from what I understand, fairly straightforward: if the adjective is before the noun, it must be hyphenated ...

But this premises is quite incorrect. Mere grammatical form never mandates hyphenation. As the linked articles indicate:

• Use a hyphen if it eliminates ambiguity or helps your reader. ...
• We hyphenate modifiers for clarity
• If a compound adjective can be misread, use a hyphen.

When the meaning is clear without using a hyphen, it need not be used. In many cases this will mean that a hyphen will be sued, because many compounds can be read in multiple ways. But long familiar compounds will tend to drop the hyphen, because other meanings become improbable when a stand compound becomes a fixed phrase.

Incidentally, the APA link suggests hyphenating all words of a multi-word compound adjective. This means that "A big-data-based product" is not only permitted, but favored. Specifically the APA page says, under "General Principle 2":

Also use hyphens for -- Compounds in which the base word is:

...

more than one word: non-achievement-oriented students