Why is Greyhawk is "Better" than the Forgotten Realms?
Simple - less canon.
The more canon one has built into a setting, the more restricted the paths of the players and the greater the chance they will be overshadowed by the setting's named NPCs.
Also, the more canon there is built into a setting, the greater the chance the players will know more than the DM about the setting, and that can never lead to a good ending. Going off the "canon tracks" can lead to push back.
Still, it does make the Forgotten Realms more ripe as a shared fiction world than Greyhawk, because there is enough canon to keep various writers on the same page.
Stupid shit that seeps into one's mind while trying to sleep at night...