What's written there seems to cover how it's defined in Japanese for the most part. I wouldn't call it poor.
"A particle indicating communication of information that's unknown to the listener" does not cover most frequent uses. It touches on one single use, and excludes most others. So while I would definitely recommend any learner to not just rely on a brief dictionary description when learning about core grammar points such as sentence-final particles, the current description in JMdict is better than your attempt. If you search for "よ" on Jisho.org, it will provide you with some additional links on the right sidebar. You can contribute to these results here: https://github.com/Jisho-org/jisho-notes
I don't suggest to replace the whole dictionary entry with my suggestion! But denoting that new information is being communicated is definitely a very frequent way よ is used and one that is currently missing from the definition.
Have you checked how it's defined in Japanese dictionaries?
"new information is being communicated"
Debatable how true that actually is. I would understand よ in that case to simply be a marker of emphasis. Speakers indeed choose to put extra emphasis where (presumably) new information is communicated, but I wouldn't say that that is somehow inherent in よ itself, just a consequence of the fact that humans tend to use language for transporting logically coherent information. Would you disagree? (I'm aware Japanese language textbooks for non-natives probably come up with all kinds of explanations for different phenomenons in the language and these might hold merit for language learning purposes but a dictionary should be grounded in more general linguistic research.)
Poor dictionary entry for よ
As a learner, I think the dictionary entry for よ is pretty poor and doesn't provide a good description of how the particle functions. Something like "A particle indicating communication of information that's unknown to the listener" would cover most frequent uses of the particle.