One key difference is that there can be multiple communities for any given topic, so you can join them all, or pick just one, or even make your own if.you dislike how the others are being run.

Sometimes people get really hung up on this being confusing or being a problem, but there are already and will be more tools in the future to group similar communities together into feeds and it doesn't feel "fractured" to me at all as it is anyways.

If anything I think reddit normalizing the concept that there is pretty much one main community for every topic has made people get used to something far less intuitive.

I think of communities about the same topics on different communities as like whales in a pod, they are independent, sometimes opposed, sometimes indifferent, sometimes alligned but no matter what you can see posts, ideas and conversations surface at similar points in time through each of them and thus there is a very indirect sort of coherency even when there are stark divisions in the community structures and beliefs.

To put it another way if something someone shared on any one particular community is truly important or worth interacting with the rest of the "pod" of similar communities will surface the same thing eventually even if it isn't from being literally crossposted from one community to the other.

A specific example of this are the communities themed around collapse on the fediverse. They don't all have the same articles/posts but the really important ones about the climate or whatever tend to make it to all the communities directly or indirectly once they have been shared in one of them.

Another much more light hearted example is how the actually meaningful gaming news and ideas will propagate around the various different gaming communities on the fediverse. The duplication creates a new level of meaning in a way.