If you think of the ravelry community as valid as an in person community this will be nicer I think.
I think both things can be simultaneously true. There are a million sub-cultures that can now exist, that are no longer tied to a geographic location. This is both good and bad. Good, insofar as if you're in the middle of Ohio in a 2000 person town, and really-really into model trains or whatever, you can find an online community that shares this. But I also think it's bad insofar as we've lost some sense of culture or commonality with our (geographic) neighbors.
But to the homogenization point; I still think within a specific sub-culture (sewing circles), you can have global homogenization. The sewing circle might new be global, on facebook and tiktok, instead of 10,000 insular hamlets. Is this bad/good? I'm not sure. There's nothing from stopping you creating a local facebook group. And in theory, good ideas can spread rather than be confined to a specific geographic group. But I can't help feeling that some independent thought and ways of thinking are lost through this globalization.
It has its ups and downs. It does mean that it's harder to mesh with any given stranger out there (unless you watch Sports, pretty much the last bastion of cable monoculture). But it also means anyone who does mesh with you probably is very easy to form a strong bond with.
But if you never find that person, the world can feel depressingly small. Hence the retreat to online communities and all its benfits and downsides.
These trends would spread slowly enough that other trends in other communities would have time and room to grow and develop. The result is you get a bunch of localized cultures, all unique in some way.
The best analogy I can think of is a plant mono-crop. Instead of different species of plant gradually finding their niche, we plant 50,000 acres with corn or soy.
I have to say, even over the last 20+ years or so, it really does feel like you can go anywhere in the world and get a very similar experience. You can go to the local 7-11, buy a coca-cola, hit up your local costco, listen to people arguing about American politics. It just feels like different countries have gradually been losing their unique culture, and we just have this global homogenized version with slight regional differences.