When Universal got the edge
Most will agree the turning point in the Disney-Universal battle was when Disney foolishly turned down the chance to make a land based on Harry Potter. It came down to the budget and conflicts of control with creator J.K. Rowling. Universal had no such qualms and as soon as their Harry Potter land opened, people went wild. It was everything Disney had once done well, immersing guests in this world with amazing detail and Forbidden Journey topping lists of the best theme park rides in the world.
This combined with Disney Imagineering in a downturn. The Imagineering Story documentary on Disney+ flat out states that U.S. Imagineers were openly jealous of how Tokyo, Hong Kong and Shanghai had the freedom and budget for rides they lacked. It seemed Disney was afraid of investing, but seeing Universal rise up with more Harry Potter and other rides pushed them on. They made the classic mistake of getting too complacent in supremacy and ignoring the challenger rising up against them. The huge success of Universal's Potter area was a wake-up call that Disney had to up the game to keep things going.
That led to the creation of Pandora at Animal Kingdom which has worked better than expected. It also paved the way for Galaxy's Edge, which does its best to make a Star Wars land succeed with Rise of the Resistance, which outdoes Forbidden Journey on a stunning ride.
There was also the Star Wars Galactic Star Cruiser, which may end up being a noble failure trying to give guests something different. Yet, seeing the last few years of budget cuts and other issues, Disney seems to be lacking when it comes to competing with Universal. Which is why the arrival of Epic Universe can be the shot in the arm they need.