WebKit and Safari have come a long way. Flowery puts browser engines through their paces with its UI animation, which is smoothest on WebKit. Safari’s OS integration (e.g., elastic scroll, Sonoma’s “Add to Dock”) is more polished than Chrome’s.
It wasn’t a walk in the park though. An early decision, after maddening attempts to circumvent browser quirks five years ago, was to build substitutes for common building blocks of the browser on mobile, notably the virtual keyboard, textboxes, and text selection. This wouldn’t have been possible without web components and Google’s excellent Lit library.