I think a lot of users on Reddit (including some who gave migrated to kbin/Lemmy) haven’t experienced a lot of the forum and IRC era of the internet.
As you’ve mentioned, “fractured” communities can actually be beneficial since each contribution is that much more valuable and nuances can actually exist between the similar communities. It allows things like the instance I’m on where I know I’m more likely to get a Canadian perspective in the communities on lemmy.ca versus other instances. To me that’s a huge feature over centralized platforms where those nuances would get drowned out.