> Who can honestly say that the best possible dev path for them (product/business) is to need Scala devs to do their JS frontend?

The ability to give a developer a feature and have them use the same language, domain model, error handling logic, business logic, serialisation codecs, tooling etc to implement it end-to-end is compelling to me.

And the number of developers who are seriously good at full-stack is far smaller than Scala ones.