I know it’s valid syntax for html. Have you seen any evidence in Obsidian documentation that a local vault path would be recognized?
An html relative filesystem path on a server and a local Vault path aren’t equivalent. They just look identical in syntax.
I agree it would be great if it worked. I’m just brainstorming why it might not be.
Example, relative images have never worked in html syntax for text links. I don’t know if that has ever changed: