Well put. I had to use Scala for a little and I wasn't a fan.
It's maybe a fun language to play around with for a pet project, but for a reliable production system I would never pick it.
The language is too flexible with too many ways to do the same thing, increasing cognitive load and making things difficult to understand. Maybe you can limit that in your own projects, but what if you have to look at a library codebase that's structured completely differently. Trying to understand that can take a lot of time.
Also there is the problem with hiring. Maybe your current team can work well with Scala, but what if a key member leaves or a service gets transferred. Hiring for Scala turned out to be impossible, so you get all these people that need to learn Scala first. Normally that may be ok, but Scala has a pretty steep learning curve so it takes a lot longer to onboard people.
On hiring: Python Paradox comes to mind (http://www.paulgraham.com/pypar.html).
I've never met sub-par FPer or Scala programmer specifically.
Using PHP or Javascript might give you a bigger top of the hiring funnel, but it doesn't mean you'll have easier time finding well-qualified applicant.
The language is too flexible with too many ways to do the same thing, increasing cognitive load and making things difficult to understand. Maybe you can limit that in your own projects, but what if you have to look at a library codebase that's structured completely differently. Trying to understand that can take a lot of time.
Also there is the problem with hiring. Maybe your current team can work well with Scala, but what if a key member leaves or a service gets transferred. Hiring for Scala turned out to be impossible, so you get all these people that need to learn Scala first. Normally that may be ok, but Scala has a pretty steep learning curve so it takes a lot longer to onboard people.