Did he forget Minecraft? It was made by a solo developer. He's now a billionaire from it and bought one of the most expensive homes in LA.
RCT was basically start to finish developed by one person with some sound and graphics work done by a couple other people.
https://minecraft.fandom.com/wiki/Java_Edition_Alpha_v1.2.0
https://blog.omniarchive.uk/post/1096322756/working-on-a-fri...
It was “quite advanced” but at the same time very much in its infancy in terms of the timeline of the game.
I personally don’t think the game would have gone as far as it did if it continued as a solo project.