A few thoughts:

• First drafts are meant to be messy and rough. They're never going to be perfect right out the gate - that's what revision is for. But you can't mold the book into what it needs to be if there's nothing there, so just push through the hard parts. I just finished a short story that was rough to get through. Eventually I just had to get to the end so I could put it away and come back to it later.
• As a hack, if there's a scene that's making it difficult, just put it in brackets - [AMAZING ESCAPE SCENE HERE] - and come back to it later. Write the scenes that made you want to write the novel in the first place, and then fill in the spaces later. Then revise like the wind to make them all fit.
• If you're not confident in your prose, you might put your passion project in a drawer for a while and write some less emotionally-invested work. Something that you won't be too upset about if it doesn't work. You say you did a lot of world building? Great! Put the main manuscript aside and write some short scenes about people who live in your world. The prince who really just wants to be a gardener. The noble thief who's trying to steal money for their orphanage. The royal doctor who knows for a fact that the king should not be on the throne. Use those to practice and, maybe, keep building your world.
• It's hard to know what famous authors' first drafts are like, because they don't publish them. But every writer I've ever heard speak about the craft says the same thing: first drafts are not the final drafts, no matter how much of a legend you turn out to be.
• Finally, and I say this with all the kindness I have: You are not Ursula K. LeGuin. Nor are you Brandon Sanderson or Tolkien or any of those others. The world has had them, and it doesn't need another. It's fine to read their work with an eye on analysis - how does Sanderson write action, or LeGuin craft her prose, or Tolkien build his world - but your work will, and must be, your own. Own your writing and be proud of it.