After using Cocoa for about 10 years and React for maybe 1-2 years, I'd say that React is way easier for visual customization and hierarchy. Cocoa's hierarchy is more efficient but at a cost of being more verbose and tedious. But Cocoa was never meant to be very easy to visually customize, since part of the Apple Way ™ is that everything looks and works the same, which was probably a reaction to the over-customization of the 90s and early 2000s, but tends to go against the grain in modern UI where every application has its own branded UI that basically requires the composeability and simplicity of HTML + CSS.

Edit: also, nobody wants or uses native desktop apps anymore, so that's a big plus for React (either via Electron or just plain web app)