It works fine for me on latest Discourse version. I can see the “Introduction” pre-filled when running the wizard again.
Yes, the “Introduction” goes to “Welcome to Discourse” topic. The content gets prepended to the existing/seeded welcome topic.
For example I entered “Welcome to techAPJ’s Discourse forum!” in the introduction step, and you can see the resulting topic here: https://discourse.techapj.com/t/welcome-to-discourse/8