Slight nit: Opacity can still matter, in modern games they're usually kicked to a different, more expensive render pass. However that doesn't really impact UIs

Slight nit: Opacity can still matter, in modern games they're usually kicked to a different, more expensive render pass. However that doesn't really impact UIs as things aren't rendered front to back but in layer order. Although opacity can have some gnarly fill implications if you go crazy with it. Overall though, yeah web stuff falls well behind more modern UI renderers like HWUI on Android and the like.