From an outline pov, asciidoc and org-mode are better than markdown. txt is better than md because it makes no assumptions about markdown syntax.
Problem with all the formatting it is that’s dependent on interpretation and so not really permanent.
When Dynalist started, rich text was popular and programs using markdown internally were not prevalent in the way they are now. No lock-in.
I can’t remember how much formatting is exported (I stopped using Dynalist some time ago), but I do remember that it was best if you typed the markdown rather than using the keyboard shortcuts.
You could set Logseq up in org-mode and import your OPML into that. Though looks as if the logseq import is broken. There’s a fair chance org-mode will outlast markdown (doesn’t have the huge number of variants) - EMACS has been around a long time.
tbh, I don’t think you can have your desired long-term permanence together with all your preferred formatting.