I agree that the UI is dated and can be a little overwhelming. The sample RFC (https://rfchub.app/rfchub/rfc1-org-batch-markdown-exporter-j...) shows what a proposal looks like with every single feature being used. Most of the time they'll look a bit simpler. I have a big UI overhaul planned but I'm hoping to get more real usage feedback on the core functionality first.
FWIW the editing process does use markdown, and the "download" link in the sidebar downloads a markdown file with YAML frontmatter to avoid vendor lock-in. RFC Hub has so much functionality that it's difficult to explain it all on the homepage. There is this overview document but it's honestly just overwhelming: