That's a hell of a statement. RDR2 is unparalleled from an open world perspective, with so many unique, hand-crafted moments, activities, and stories to stumble upon. No other game has achieved an open world as organic as RDR2, and while I haven't yet played GoT, every review and impression I've read seems to state that its world is repetitive, saturated with filler collectibles that are all exactly the same, and with side quests that that are rote go-from-A-to-B quests with little to no interesting characters. That doesn't seem like the kind of world I would put ahead of RDR2.
I love RDR2 (and obviously it was sitting at second best game of this gen for me, until 2020). I never platinumed it (thanks to the tedious collectibles), but I have 80% of the trophies, and I played a heap of Red Dead Online as well (I'm level 287). I know the map like the back of my hand.
RDR2's open world is amazing, and the hand crafted open world events are great (until you start to see the same ones repeated over and over). I actually think The Witcher 3 has it slightly beaten in terms of the world feeling alive though: it's really hard to put my finger on why, but Novigrad just feels like a real, breathing city more than St Denis. RDR2 does a great job, but the NPC's still feel a bit 'gamey' for me, like they are cardboard cutouts that will disappear as soon as I ride away. I don't know how The Witcher 3 does a better job on that front for me, but it does.
If we're talking about collectibles, then RDR2 is unfortunately the game that is filled with the tedious fetch quest stuff - I'm ok with that stuff up to a point, provided it's drawing me to unique and interesting spots on the map, but RDR2 just ends up taking the piss. GoT is very understated on that front, with the fox/bird elements making them feel a lot less like a checklist, and unique gameplay elements like the haikus and shrine platforming making them feel very handcrafted, rather copy and paste.
From a central story perspective, RDR2 has GoT beaten hands down (and frankly had every game beaten hands down, until TLOU2 came along). But GoT still has a great story, with an interesting antagonist (better than Micah or the Pinkertons IMHO), great character arc, and meaningful ending, and the side story writing was actually brilliant: the Ishikawa and Masako quests are fantastic, and the Norio quest line really ends with a bang too. Yuna, Ishikawa, Lady Masako, Tomoe, and Kotal Khan are all great characters, and well written.
On the graphics front, I'd actually call it a draw. RDR2 has amazing LOD, DOF, and motion blur, that all work together
just so to hit it out of the park. Amazing tech. But GoT pulls it back with its stunning lighting and art direction in the open world. I occasionally took screenshots in RDR2, but GoT had me using the photo mode like a fiend, something I
never do in any game.
Which brings us to the final element, where GoT is able to show RDR2 a clean pair of heels and in turn manages to get its nose in front overall: gameplay. RDR2 has a lot of gameplay concessions to story. I understand that choice, even if RDR2 went way overboard with silly choices like the literal camp chores. But GoT prioritises gameplay (also a valid choice).
GoT succeeds because the gameplay is absolutely incredible. Where the RDR2 controls (especially gunplay) so often felt like they were getting in the way, and honestly killed my desire to replay the game, the GoT controls are an absolute joy. I usually hate 'horde mode' gameplay, but the combat in GoT is just so fun that I've found myself getting to max level in Legends, playing a heap of 'horde mode' gameplay. The trump card that GoT has is that unlike RDR2, it's
really fun to play. I'm actually not one of these people who think that a game can only be fun; like other forms of entertainment, there can be a heap of value outside just fun (it can be thought provoking, atmospheric, immersive, emotive, etc.). But it's a huge factor in why I rate GoT better than RDR2.