They've followed through on their promises so far, and you can actually self-host pretty much the whole stack today:
https://alice.bsky.sh/post/3laega7icmi2q
I'd perfer for mastodon to take off personally, but really at this point both are good options and worlds better than twitter.
And, if you help someone register, take a look at all the instances! It's more healthy for the network if everyone isn't siloed on the few larger ones.
The structure of the fediverse (lemmy/kbin/mastodon etc) makes it really difficult for alt-right and troll instances to find a meaningful presence.
Truth Social for example is just a mastodon instance, but everyone immediately defederated (blocked) them, so they have no reach. Hateful ideologies want a large audience on which to inflict their bullshit, and the federated model makes it really easy to cut them off.
You can run your own relay, though:
https://whtwnd.com/bnewbold.net/entries/Notes%20on%20Running%20a%20Full-Network%20atproto%20Relay%20(July%202024)
I do prefer Activitypub overall, and it's certainly more mature, but any efforts towards decentralization should be encouraged/celebrated.