I think you are right for the most part. I assume that some big servers will take most of the users and that the cost of maintaining the fediverse will become quite high in one way or the other as the network grows and the malicious actors gain incentives to interact with the network.
I think the fediverse is more like the old web. I don't really consider my data very portable, but my ways of consuming and interacting with the content is. I for one don't really care if my posts go with me if i move somewhere else. If my home server defederates, then I can move to another kbin instance and my experience remains much the same. The monolithic singular identity that I can take with me wherever I go isn't something the fediverse delivers on right now, but that is fine.