Scala is a fine backend language, with far more bells-and-whistles than Java 8.
However the comparison beyond language features is very much relevant, including the lack of Android support in Scala 2.12
Adding to the woes, the code emitted by 2.12 is slower ( https://news.ycombinator.com/item?id=12066653 )
Not to say things can't improve. After the initial announcement of 2.12 at ScalaDays 2015 and 2016, expect more at ScalaDays 2017.