If Rockstar also doesn't understand that, then who does? Nobody? You?
Piranha Bytes at least used to. Perhaps the Saints Row developers too. Fallout was of course a superb open-world game, if not in the sense we understand the term nowadays, and New Vegas was really good too (in some ways even better). And as much fun as it is to bash Bethesda, I do like their approach to open worlds, even though they have the bad habit of sticking all of their content into underground dungeons and have made some massive blunders regarding the mechanics of their games.
It's fun to cause havoc in GTA, and all of the games have some really cool and memorable missions, but it has always pissed me off how the games insist on putting you on rails and prevent you from using any sort of creativity in achieving your goals. When you start a mission, you feel like a movie actor trying to follow a script that was written by someone else, and only rarely do the games allow you to do things in different ways based on your own preference. It's kind of the opposite of the Ubisoft model where you're generally given a lot of freedom but where most of the content is so damn generic and repetitive that it sucks away your soul. If you've got an open world,
use it in your mission design. This goes double for those developers that want to make an RPG, where it generally should be possible to do things in lots of different ways.