Most negative comments aren't mean-spirited, but they can verge on nitpicky. The worst type of comments are not those talking about product shortcomings, but are ones that veer way off topic into a commenter's pet point and kind of tank the whole discussion. Similarly, if everyone's just praising a product its not particularly constructive or helpful, except to know the product is going in the right direction. Good critique is super valuable.
This isn't necessarily because people who think they're smart are melancholic. I think it's because praise ultimately sounds the same in the end. Because it sounds the same, it doesn't sound smart, it doesn't get upvoted, you're better off just not posting it.
On the other hand, you can sound smart and original with criticism if you word it right.
Hence why I take the critical comments with a grain of salt and pay attention to the fact that the original HN post is on the front page with 256 points at the time of this writing. A lot of people clearly really like Notion.
I'd recommend watching their office hours video for building things from scratch to see how powerful it is for personal use: https://www.youtube.com/watch?v=x1I3Hic0urY