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.