So you weren't actually using the thesaurus as a reverse dictionary here. The thesaurus contains definitions, and the reverse dictionary was the search tool built into their website. It would work just as well against a dictionary as a thesaurus.
Importantly to the point being discussed, what you did does not work at all against an actual physical thesaurus book.
If the thesaurus had an entry for "very useful" (as WordHippo does), then yes, it would work against an actual physical thesaurus book. This whole cluster of words is coded into Wiktionary incorrectly – for example, https://en.wiktionary.org/wiki/utility#Synonyms is a subsection of "Adjective" despite listing synonyms for a sense of the noun:
> (state of being useful): usefulness, value, advantages, benefit, return, merits, virtue, note
where "note" is a synonym of distinction, not utility, and Thesaurus:utility has fewer entries than this. Versatility should be listed in Thesaurus:utility as a related concept.
Paper thesauruses (thesaurai?) won't have prefixes like "very" in their pages.
Furthermore, even if we allow "very useful", that's a far cry from "admitting a large number of uses". The latter requires a search engine to properly map.
Which they've been good at for a while. You could have googled "word meaning admitting a large number of uses" back in 2018 and gotten good answers.
My point is, the tools you've linked to are useful/versatile, but it's not the thesaurus that makes them so useful, it's the digital query engine built on top of the thesaurus.
Even if I don't know the word "versatile", I can go from the phrase "admitting a large number of uses" to the phrase "very useful". The original point I made (before I discovered OneLook Thesaurus) described the effectiveness of a procedure that was just manually looking things up in databases, as one might do in a paper thesaurus. (I could print out Wiktionary and WordHippo in alphabetical order, buy a Cambridge Thesaurus and some bookshelves, and perform the procedure entirely offline, with only a constant factor slowdown.)
Importantly to the point being discussed, what you did does not work at all against an actual physical thesaurus book.