The point of furigana is to be exact - it's a pronunciation guide, and its purpose is to distinguish or to teach. If it's wrong, then nothing makes sense.
If I asked you 'are you a sewer (pronounced "soo-er")?', would that make sense? Maybe if you looked at it hard enough and thought about it, but in the meantime, I would probably get some very strange looks for asking.
It's funny to see LLMs being mentioned, because this is yet another case where "good enough" is, after all, not good enough once you know how "good enough" should be.
As far as I know, all the automated options out there (wether it's Furiganator, the chrome extension, or Google Translate's pronunciation) are far from 100% accurate. I still find both to be very useful, I just don't rely on them to be the absolute truth; they still help me on a daily basis. The web page for this font mentioned it didn't show any furigana if it was ambiguous (I haven't verified),and someone else here mentioned it was ~80% accurate. I respectfully disagree with the fact that it's useless if not perfect; I've personally found all these tools useful, and have not learned a single "wrong reading" because of them because I don't use them as a tool to learn kanji readings to begin with.
Yomitan only shows readings for words you explicitly hover over and press a modifier key, so it doesn't distract you, and when you do explicitly ask for a word, Yomitan will show all the readings and definitions.
I'd agree that 80% is better than nothing if you have no alternatives, but you do. I don't know about Furiganator, but Google Translate is also much better than 80%.
For that matter, furigana are commonly used to deliberately override ordinary readings. In some cases, it's more like kanji are used to explain the meaning of some katakana (especially, say, in-world jargon in a video game or LN) set as furigana above them. (Or some hidden or unusual connotation of a common word in hiragana.)
If I asked you 'are you a sewer (pronounced "soo-er")?', would that make sense? Maybe if you looked at it hard enough and thought about it, but in the meantime, I would probably get some very strange looks for asking.