Regardless of the source I think the main point folks are missing is that a lot of DE jobs will require you to know Scala so it's a good tool to have if you want to be a DE somewhere.

SQL is also an amazing tool and you should definitely learn if but there are a lot of DE jobs out there with Scala in the "Requirements" section of the job listing. Parts of the industry might be moving away from it, but if you're looking to make a jump into DE I think you're hamstringing yourself by avoiding Scala.