Yes I don’t understand the point of misskey either. It just seems to be a Japanese clone of mastodon with a small, differing interpretation of some parts of ActivityPub.
Sublinks exists because the developers of Lemmy have repeatedly ignored feature requests from instance admins and acted in a hostile manner towards them. They’re unpleasant to work with, so a bunch of people decided to no longer work with them and create their own project.
It feels like you’re only capable of seeing the “logical” point for something to exist friend. Misskey is to Tumblr as Mastodon is to Twitter.