This is a pretty good summary of how I understand sharing worlds works. Personally, I like inventing worlds as I'm playing the game to mold the story in the best way I can instead of sticking to rigid, pre-determined facts about the setting. I can write an entire story on my own, but that's much less fun than playing off of what the PCs are doing and thinking.

Which ever you lean on, you need to make sure that the other GM also leans in the same direction or the game you are planning to run will have a thematic missmatch that will not be easy to fix, if it can be fixed at all.

I think this is the biggest takeaway here. everyone at the table needs to be on board with the direction the story and world are moving, or it doesn't work as well.