I have the same perspective - to such a degree that any time I see someone post a notebooklm I wonder if it's paid advertising. Every time I've tried it on something like a whitepaper etc. it just makes stuff up or says things that are kind of worthless. Reminds me of ChatGPT 3.5 in terms of quality of the presented content.

The voices sounded REALLY good the first time I used it. But then sounded exactly the same every time after that and became underwhelmed.