I don't think this project is necessarily going in the wrong direction, but I agree that keeping track of web URLs requires more data than just the URL and title.

At the very least, I personally need tags. Tree hierarchies are too limiting, but tags allow adding free-form metadata which can be used to quickly find anything. I often don't remember the actual URL or title of a web site, but I'm looking for a general category, and with tags I'm usually able to find what I'm looking for. This does require a certain level of discipline from the user to use tags consistently, but they work well IME.

These days with ML tools it's easier than ever to assign relevant tags to URLs automatically, though I would personally not rely on them because of their propensity to hallucinate and not follow conventions.

And, like you say, web sites change and disappear constantly, so snapshots are important as well.

I've been meaning to try SingleFile/ArchiveBox/Wallabag for months now, but I'm currently too comfortable with Pinboard. Pinboard has been working great for me for many years, contrary to the negative buzz around it, but I don't have confidence that it will stick around forever. I just hope that I can export and migrate all my snapshot data as well...