I never got into them either before Obsidian. I’d’ve said (I did say) I don’t get on with outliners. But that changed when I found I could have a nice local file store and simply use the outliners to enhance some of the processing. The markdown files are the bedrock, but they are somewhat rigid and slow. So I can add faster movement while still keeping the bedrock.
You are correct in that they are effectively online databases. Just as Obsidian is online notes if you use a sync solution.
Dynalist does have a local option (Pro only) - though I’ve never used it.
Or, you can do what I do, which is to bounce an opml in, edit, export, delete. Online but not for long.
Personally there are a few things I want local only, other I want local most of the time and more when I don’t mind so long as the online security is good enough.
I’m sure there are other outliners where this would work including many which are local only. But I’ve not tried them, though I would if I wanted to use this workflow with a local outliner. The key is opml and the ease of importing and exporting it.
PS
One of the big attractions for me is the kanban view in Workflowy. The whole note, or specific headers, can be toggled between outline view and kanban view.