My stock thought is that within a few years Disney will have added three entire lands (Pandora, Galaxy's Edge, Toy Story), another four new rides outside the new lands (Guardians, Ratatouille, Tron, Runaway Railway), and new restaurants in both parks and hotels.
Universal has largely only been able to create new rides from old ride locations. Universal was only able to add new capacity by creating a new gate.
But the aggregate of what Disney has been doing *is* most of a new gate. Other than Runaway Railway replacing Great Movie Ride, it's all "new" stuff that absorbs people, which is most of what people want in a 5th park ("it's crowded and people need places to go").