My personal opinion here. We (NodeBB) decided to go with categories from the get go because it was a form of hierarchy that worked well for YEARS, and you don't go breaking things that work fine.

IIRC Discourse started without categories. The whole "bucket of messages" shebang. It did not go well, in the sense that I believe people kept asking for categories.

There's something special about a curated list of folders to slot messages into, that tags and labels don't quite capture.

Or to put it simply, most people are disinterested in most things. If you present them with most things, they will be mostly disinterested.

A little defeatist, but correct in its own way.

I prefer to look at it as "each person is interested in different things, and they mostly don't overlap with any other one person, statistically".

Currently, the user is being presented with most things, so I think my framing matches the actual user perspective with better accuracy than a cheerier wording. ;)