That’s true, the -keys are certainly closer to Twitter than to Lemmy / Reddit.
But even Mastodon can follow hashtags, the interesting thing about the -keys are imho the Antennas / Newspicker, with which you can set up individual timelines with your own search word combination. This makes it less user-centred and more related to topics / content. And at least you can display ‘load conversations to replies’ in the timeline (in Sharkey). This means that the post snippets are not displayed without context, as is the case with Mastodon, but a part of the thread is shown in the timeline.
As a result, threads from Lemmy are also displayed somewhat better in Sharkey than in Mastodon, where all replies arrive separately.
The Channels in Friendica are similar to the “antennas” / “newspickers” in Misskey / Sharkey. Both are very good ways to receive content sorted by self-defined topics.
If you are looking for a way to *send *to different topics, Friendica’s (connected) “accounts” would be suitable for this, But Hubzilla offers more options for this
Friendica offers a connector for Tumblr as well as for Bluesky. Ad hoc I can only find a German-language manual for it: https://friendica-hilfe.gitbook.io/friendica-hilfe/basics/bluesky-tumblr-und-weitere-social-media-dienste