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.

You're underestimating how wrong this is going to be on average. This is going to be nonsense like half the time. It's not comparable to Google Translate, it's more comparable to Babel Fish circa 1997.