Bluesky adds 700,000 new users in a week / A ‘majority' of the new users are from the US, indicating that people are searching for a new platform as an alternative to X.
I think it's the opposite. On Mastadon you can make a new account on a better server ie mods more aligned with you. On bluesky if you make a new account and say a similar bannable thing again you'll be banned again.
It doesn't need to be, as long as there is also a proper default for those who don't care. Lemmy and Mastodon both unfortunately lacked this during the periods where they both had the most opportunity to grow.
Nowadays Mastodon does it pretty well. Users don't need to know anything, they just download Mastodon from the app store and register on the instance it chooses by default.
Maybe you're already aware, but bluesky doesn't operate with instances like in ActivityPub land.
I've seen many people I believe are using their own PDS, but yes, discoverability is likely better because a relay is meant to aggregate and share all data it can (look up "bluesky firehose").
P.S. Mastodon's devs are part of a new initiative to improve this area of the Fediverse. Because it's so recent, we'll have to wait to see how it goes.