Please tell me you never played New Vegas or Wild Hunt.
If you're talking open world, then GTA is king.
New Vegas suffers from being a mediocre FPS, which becomes way too tiresome in the 40 hours or so that you play it for.
The Witcher has one of the most tedious combat systems I've seen. It's like playing Batman: Arkham Asylum but less responsive, less options, less mobility, and no real difference between fights early in the game, and later in the game, other than you do a bit more damage and your enemies are tougher. There's no progression in Geralt's combat skills to match the progression in the narrative. I got bored of the Witcher 2 long before I finished it, and I just can't get into Wild Hunt.
At least in Inquisition much of the open world stuff is skippable, and at least the story, centred around gradually building the Inquisition's forces, matches the exploration and side-quest-iness of the gameplay. And, it was a response to criticism of DA2 (though they went overboard).
One of the most important aspects of an open world game is the ability to offer a consistently interesting, yet varied moment-to-moment gameplay. There's no point in going from place to place if the gameplay is the same everywhere. This is why I get bored of the Witcher: almost all of what you encounter in the world outside settlements is enemies, and you can't interact with them in novel ways because of how limited the combat is. GTA, however, does this amazingly with its mix of driving, shooting, and all the other things the game asks you to do.
Open world and RPG don't really mix well, because the openness of the world destroys the pacing of the narrative. So you get ridiculous dissonance like Fallout 4, where a narrative of great urgency (your son has been kidnapped) is completely undercut by a game design which encourages vacillation. But GTA was really meant to be like the protagonist's lives - you'lll switch to them and see Michael on a bench somewhere, or Trevor walking down the street - that level of naturalism in the storytelling stops it feeling like the exploration interrupts the story, because the story is interrupted by the characters living their lives.
GTA gets around this because its world is so minutely detailed that exploring it for the sake of exploring it, not for loot or challenges, is genuinely interesting and fun. If there was no loot in Fallout, nobody would bother exploring. If a game has to use material rewards to encourage you to explore its world, then it shouldn't be an open world. Unless you're Dark Souls. Then you can do what you want.