True. But in due time you’ll end up in situation where few of these (or maybe even one) becomes the “go to” community, because it has best/largest discussions - just like on Reddit. We’re still at the start of this journey. Also, the other instances are their “own thing”. Maybe that’s fragmentation, but essentially they might be aimed for completely different demographic (the users of that particular instance).
while technically you’re correct, what I see as different that I think needs improvement, is the discoverability. It is needed to somehow when I search for e.g. technology to also see the various federated “technology” communities. If I have to manually search for an instance, find the correct handle, then go search for this handle in my own instance and only after that to be able to subscribe, it adds a difficulty on the level that I may never manage to know about the existence of some other communities (magazines). Apart from that, I agree it is totally fine to just let them organically grow and it will sort itself out on which one I may want to participate more.
you missed the point where the open source devs were in a constant race to adapt to all the google-“innovations” and actually troubleshoot on them which ends up demotivating