Yah, the one thing that I like about bluesky is their name-spacing: “sports.npr.org”

We are coming full circle back to Usenet.

I like the Matrix format, "@user:domain.tld"

I prefer the email format: user@domain.tld. There's no reason that can't be used for social media.

it was annoying to me to type it too! There are also webfinger URLs that serve the same purpose like https://mastodon.social/@gargron == @gargron@mastodon.social

That's not a WebFinger URL. WebFinger URLs point to /.well-known/ path that returns a JSON document with links to other places for the user. To simplify WebFinger use by a human, we introduced acct:user@example.com syntax. And (at least my) WebFinger clients can assume the acct: part, much like email clients do for the email: scheme.