Depending on how loosely you want to define "functional", I'd argue Javascript is more popular.
There is a lot of merit in just using Scala as a better Java, in fact a lot of its original popularity was that kind of adoption. These days, however, Kotlin is eating that cake, so maybe it's true now?
I'd prefer something that compiled to machine code anyway. Scala also has type erasure unpleasantness due to its dependence on JVM.
Type erasure isn't just a JVM implementation detail. Haskell, for example, has no JVM dependency and relies solely on type erasure (a running program can't introspect type information). Not reifying types at run-time (in this case type parameters) is a legitimate implementation decision as reification has non-trivial costs.