Ding vs Fabiano is +6 =10 -3 (including 2 wins with the black pieces)
Nepo vs Fabiano is +7 =21 -2 (including 3 wins with the black pieces)
---
I think a lot of what we're seeing is not about openings, but risk tolerance. Fabiano has incredible, and fighting, opening preparation. But what really matters is what happens after the opening. In high level chess you often find yourself in a scenario where you see two main ideas in a position. One gives you slight winning chances, but basically zero losing chances. The other gives you good winning chances, but the position will be complex and difficult to play - your opponent will also have plenty of winning chances. And Ding, in particular, seemingly had just zero fear of risk this entire match, which is largely what drove everything.
I'd also add this drives another common misconception in chess. If two very strong players both play a game while making a conscious effort to avoid complexity, you'll end up with a draw that has an extremely high level of accuracy. By contrast if they decide to enter into these sort of unclear positions, you'll see even the best in the world make mistakes, and even blunders, because chess is hard! So people outside the game see the mistakes as driving the results, and that's certainly true. But the reason those mistakes are happening is not because the players are just playing weaker, but because even the best in the world will make mistakes in complex positions.