The point I'm trying to make is that a huge portion of what makes Elden Ring's exploration so great is the thrill of it. There is a sense of dread and imminent danger just like in their other games but you're free to go wherever you please. When you step inside a cavern, you don't know what enemies lie inside. When you opened that trap chest in Limgrave and got transported to Sellia Crystal Tunnel in Caelid, you went WTF and when you started getting wrecked by enemies 50 levels higher than you, you remembered it. The fact that From games are notoriously difficult makes the exploration that much better. If you remove that, the impact of delving into unknown territory would be significantly lessened but this is independent of the game being open-world.
BOTW is an excellent case of open-world design because it does make something of its open world. You have mechanics like thunder, rain, and other weather effects. You have tools to interact with the world and exploit the physics, you have events based on weather conditions and time of day, etc. What BOTW does with the open world couldn't work within the traditional Zelda framework which banks on rigid levels and pre-determined conditions with a somewhat linear approach. Put BOTW in a non-open world, half the shit isn't nearly as interesting because then you'd be restricted to using your items just to solve the usual puzzles like you do in every Zelda. BOTW exploits its open-world. Elden Ring doesn't really or at least not in a way that's noteworthy.
Take out the open world of Elden Ring and keep only the legacy dungeons, the game is still amazing. Take out the open world of BOTW and I'm not even sure what you end up with. Elden Ring took what already worked and added it to an open world. BOTW on the other hand reinvented itself thanks (or some would say because) of to the open world. BOTW is more sandboxish. Elden Ring is more traditional.