Obsidian is just an editor for markdown files, Hugo is open source. If we can't count open source as "self-owned" then god no one owns anything because pretty much no one runs their computer on a OS they build from scratch with no contributors or using any existing code.

The idea is to use them as tools that get the job done and get out of the way, while you own the content. All of these tools are easily replaceable and the pipeline can still publish to the final blog domain without any worry.

Obsidian is just a markdown editor, so the files are portable. The context is that the content and methods to publish it are not someone elses.