Lots of things have changed since es5. It's actually more than suitable for front end. I am certain that by using react/redux and es2017 you could cut pretty much any native codebase in half and still have it appear and behave cleaner in the end. This is why they are porting these principles to native, for instance in Kotlins Anko, Litho, ComponentKit, ReactXP, or react-native itself.

JS + npm/node also has more modules and components to choose from than any other repository combined. The crippling factor was always the browser, now that that's out of the way, it can build applications native counterparts could not get at given the same amount of money, time and workforce.

Actually looking at examples of the apps shown here JS does not matter. They still look like webviews. Cross-platfrom is really a misnomer, it should be no-platform. Yeah, it kind of runs on both, and alien on both too.