I think it is a case of, it is easier to find those niches nowadays but when you do it is a more shallow and controlled version of said thing.
On the old web, you would just stumble onto something deep but the barrier to get to it was fairly high. It could also just be total nonsense but at least you could see the passion behind it.
I agree with your general take. People talk about the old web as 'the good old days' but it really wasn't that great. I do have some fond memories of the mid 2000's when it was all starting to mature but also before corporate capture took hold. Even then, you would just end up stumbling around blindly most of the time.
Niches nowdays are far deeper and more vibrant than they were 20 years ago. Instead of 1 guys website or 1 fourm with 30 users you now have many discord servers with 1000s of users talking in real time, youtube channels putting out videos and making money, reddit/lemmy aggregating content, the community interacting in real time and building what it needs.
And they have to self censor so they don't get banned off those platforms.
There are so many piracy discords where you can't ask how to pirate something because that's against discord rules. I mean really? Why are you using it then?
Most niches dont have to self censor. Even the ones that do still have no trouble communicating their message. I follow a lot of military channels and they post uncensored versions of their videos off yt but there is little reason to go because seeing the gore is not why im watching the video. I still get the entire value of the video from youtube even though you might argue its self censoring.
There's a lot of people who want to talk about things like Gaza or Luigi Mangione more, but can't because of platform rules. The new web has been successful at changing society at large by preventing discussion of these things. Even here on HN I have to be careful how I describe this effect, because an account that is flagged a few times in quick succession is automatically rate-limited, which is effectively a ban.
Edit: it's not just about a niche being forced to censor, it's also about everyone being forced to censor talk about that niche. In a video games discord you couldn't talk about piracy, no matter what the owner thinks about piracy, he'd be forced to ban you for talking about piracy or else he would be banned.
There is plenty of discussion on Gaza or Luigi. If you find youself being "censored" consider that your views and "solutions" are far outside what is accepted on the platform. On the old web you could also get banned if your views did not align with the platform.
Dont compare wanting a pro terrorism fourm with niche interests its so disingenuous.