Why would the browser render engine slower than the Java Android UI render engine? I am almost certain that the browser css engine is better optimized than the

Why would the browser render engine slower than the Java Android UI render engine? I am almost certain that the browser css engine is better optimized than the Android native render. IOS is a different story since their render engine is heavily optimized against their own hardware. But still I know that webapps can have the same performance as native apps. And the end of mobile native UI kits will finally arrive. Webapps/spas will take over.