Or everyone will put in about the same amount of work making about the same amount of game stuff and the GM will at least in principle have more bandwidth available to run the game and make appropriate and engaging decisions. That's been closer to my experience.Well, don't know about them games.
The OP mentioned the long, hard work a typical GM puts into making the setting of an RPG. While the players just relax and make a single character.
So if you reverse that, each player will do the long, hard work, and the GM will make just one single simple thing.