I'm not really convinced that discovery was a problem with the old forums. There was no insatiable need to know where everything under the sun lives. You'd typically just follow a few forums around your interests. I think it became a glaring disadvantage when Reddit introduced an overabundance of options and allowed everyone to subscribe to 20 things because they could, not because they needed or wanted to. I think Reddit's value-add was community moderation without self-hosting.

This is akin to online dating. Nobody needed 5 dates a week 20 years ago and because it's an option now doesn't mean it was a problem than. Optionality is just a byproduct of social platforms.