I'm a genuine enthusiast of the One True User-Owned Datastore model, although I've found current models of that to be offputtingly obtuse in deployment terms
(I mentioned Solid earlier - see https://solidproject.org/about) - let alone for laypersons.
As someone currently operating three different ActivityPub servers (Masto, GTS, WriteFreely), the fact that user data is still siloed on a per-server basis is a weak point, as if the server goes, the user loses that data. (Which I can solve by running my own servers, but the data remains on its home server. This has both advantages - I like specialisation and compartmentalisation! - and disadvantages, in that siloed, non-transferrable data becomes particularly sensitive when you don't run your own servers.)
In an ideal world, I'd like to see user-owned data stores that could be plugged into ActivityPub on a protocol level, although I suppose that's not something that's going to be on the AP roadmap as it's fully mature now, but instead something that falls under the Spritely Project's area of interest for the next generation of open, federated protocols.
I don't think the AT Protocol successfully overcomes the user accessibility to data stores problem. (And I've no interest in touching Bluesky and its projects for a variety of reasons.)