I think that's an overstatement. I use tags regularly to find bookmarks in Pinboard. They work well since the content was curated by myself. I can find categories of links which can be further filtered into subcategories, etc., until I usually find what I want. It's a great way to have a collection of things I found interesting at some point, and tags and full-text search are useful enough to find them again when I need to.
Would I like a RAG type of interface over my bookmarks? Sure. But it's absolutely not required to have a good experience.
I think a better system wouod be one where the bookmark stores either the "link source", i.e. backlink to the site you found the bookmarked link on, or the "search term", I.e. what you were specifically looking for when you bookmarked the page.
However, with the disadvantage that I do not use the search in the browser, but the search of the operating system.
https://news.ycombinator.com/item?id=38421121
Also adding that Markdownload is awesome.
Tags and folders aren't even close to solve the problem of surfacing bookmarked links when they're needed.
And the only way to fix this, is to have them integrated into search. "You're looking for how to do X? Here's what I found on the internet. Also, you bookmarked these links about this topic, so check them out."
That, or a RAG based solution.