I'm confused. You said 3rd parties can't do official settings. I said they can, per the DM's Guild. And now you're saying that doesn't count because it's not official? I'm confused, because 3rd party has never "truly" been official. That's what 3rd party means.
DM's Guild is new, and IIRC, hasn't been done before in the industry. It's always been one-off 3rd party licenses. Now WotC is saying they give their support for all 3rd parties, and is allowing people to use their IP. So everything on the DM's Guild *is* 5e D&D
Personally I would not put my own Campaign world on DMs Guild because that would be effectively giving WotC all the rights to it. Would not be worth the price just to get an "official" stamp.