With ActivityPub, because running an instance requires hosting the data, the application, and dealing with all the subsequent scaling challenges, you kinda have to choose between being taking on active ops responsibilities or tying yourself to someone else's instance (which will probably be one of the bigger, more centralized ones).
If you decide you don't like an instance you picked and decide to move (unless things have changed) you're kinda stuck needing to start fresh.
With AtProto, it's trivial to jump ship to a different application platform and continue using your same identity. Exporting your data from a platform and self-hosting is a bit of a UX challenge, but at least it's possible.
As an example, I recently started using Tangled for the first time and was able to login using my existing bsky-backed domain (h14h.com). No need to create a new account or pick a new username -- it was as if I were already there. Then getting set up w/ self-hosting my git repos on a VPS was an afternoon of work at most, and it's just some backend service chugging away that I almost never have to think about.
The worst that will ever happen is I see a banner message in tangled.org saying something like "your repo is out of date and may be compatible with the latest version of Tangled", which I can solve by simply rebuilding & redeploying a docker image w/ the latest versions.
Granted, AtProto is definitely harder to wrap your head around architecturally. But actually interfacing it with a user is much simpler, IMO.
A good measure for decentralisation is: Can your community continue using the service if the rest of the world disappeared? Can you still federate with other communities that might still exist? What else needs to remain for the service to remain useful?
With mastodon, all of that is trivially answered. With AtProto, I'm either 100% reliant on bluesky, or I'd need to spend tenthousands of dollars a month minimum to self-host the relays and app view.
Everything I'm seeing about hosting costs in the current day and age is that the full AtProto stack (PDS, Relay, AppView) is roughly in par with hosting an ActivityPub instance of equivalent size (if not a little cheaper).
And with AtProto, folks get to pick and choose what slice of the stack they wanna host, and opt-in to more of it gradually as they see fit. With ActivityPub, you are either opting in to hosting an entire instance, or fully reliant on someone else.
I'm open to the idea I'm misunderstanding some aspect of ActivityPub, given I've not really explored the hosting side of all that deeply.
My self-hosted mastodon server continues working, and can continue federating with e.g. chaos.social
With bluesky it's different.
If I am fully self-hosting the entire bluesky app, I need to spend ten thousands of dollars a month, but it'll keep working.
If I self-host my own app, it's cheap and keeps working, but I can only see content from my users in the best of times.
If I use bluesky's relays, it's cheap and shows everyone I follow, but it'll stop working if bluesky disappears.
> If I am fully self-hosting the entire bluesky app, I need to spend ten thousands of dollars a month, but it'll keep working.
That strikes me as a point in favor of AtProto for decentralization (unless it's possible for others to cheaply/simply run their own backups of the entire mastodon.social instance & I'm just unaware of that fact).
> With bluesky it's different.
The key AtProto differentiator I find most compelling (which it seems you omitted from your list) is that Bluesky can disappear tomorrow and, if I'm running my own PDS, I can simply log in to another different platform using my same username & account and immediately see my entire message history w/o skipping a beat.
From the standpoint of an individual user who just wants to own their own data w/o needing to worry about hosting entire apps or manage scaling, the fact that AtProto allows me to host a PDS and do just that while still using any of big-name apps w/o needing to create new logins and fracture my online presence feels like a far more pragmatic trade-off, IMO.
I guess it comes down whether you care more about data decentralization, or platform decentralization. Personally, I care far more about the former, and to that end the AtProto model feels much easier to set up & far more seamless in practice.
FWIW, in the AP world there are several individuals and small teams running relays/mirrors/caches/AppViews and so on -- but you're right that this could get more expensive as things grow.
I prefer AP for one reason, it's more accessible to the people. I would prefer to see small computer organisations with member fees, and donations, that run their own little node, instead of huge monolithic components.
That's why I never liked bsky, because it was too monolithic. I never liked the monolithic AP instances either. If we're going to decentralize, let's properly decentralize.
As soon as something becomes huge and monolithic, it's a red flag.
AT doesn’t just give consistency, but a shared data model across apps. So apps can reference and render content from other apps. It’s really kind of like a web of typed JSON. Different apps are lenses through which you can see the same network. Anyone can build new experiences on top of old data. There’s nothing remotely equivalent in AP.
AP couples data to apps. In AT, it’s more like there’s one global database with entire world’s data that every app can query.
I don’t understand why the discussion always bumps into Relays. Running a Relay if you want to is cheap-ish ($30/mo) these days. There’s multiple existing ones (Bluesky or community) you can use for free. And many apps don’t use one at all and rely on community indexes like Constellation (https://constellation.microcosm.blue/). Some don’t even run their own server or database.
But really, I actually would argue the opposite: ATproto is (or at least, wants to be) more decentralized.
In the ActivityPub world, identity, application, and hosting are intrinsically linked. If I want to use Lemmy, I can either register a second, permanently separate ActivityPub account on that Lemmy instance, or ONLY use Lemmy to the extent my Mastodon instance knows how to send messages that Lemmy understands. EVERY new ActivityPub app is a new set of interoperability concerns, because each app owns its own identity and hosting. There's no way for my self-hosted Mastodon instance to provide an identity to a Lemmy server and then for that Lemmy server to tell that instance to host content on my behalf.
That's the bare minimum you'd need to match ATProto, at least in the version being told to me by the ATProto people. No idea if any of it applies to actually-existing ATProto, in the same way that actually-existing ActivityPub can't interop the way ActivityPub supporters claim it can.