I guess it depends on where one comes from. If one compares Scala to Scheme, sure, Scheme is ridiculously simple compared to Scala.

But if one compares Scala to languages which are actually used in the wild like Java, C#, PHP or C++; Scala's footprint is just incredibly small.

All of the features you mentioned are available in languages like Java or C#, too. The difference is that in most cases the implementation is so poor and incoherent, that the feature is next to useless.

I guess one just "sees" more language features being used in Scala, because almost everything which ships in the language makes some sense, while in Java/C#/PHP/C++ you have tons of utterly useless "features" which don't add any benefit, but still force people to learn them in case somebody else used them.

I have never seen "On a sufficiently big project with one or more extra clever developers most probably every feature will be used" happen in real life. In my experience one of the strengths of Scala is the way one can use some advanced feature where it makes sense, without having it bleed through the whole code. Compare that with Java's, C#'s "Oh, you used some complicated Generic type over there? Guess what, we will make every user suffer from it throughout your whole code base!"

In a sense, I prefer a language (Scala) which ships with 100 features where 90 of them make sense to a language which ships with 400 features where only 50 make sense, like C# (multiply "feature" count by 10 for C++).

  > And I don't need a compiler to catch errors that a unit test would also catch.

Well, using the compiler means that it will also catch errors which you haven't written unit tests for. Tests can't prove the absence of certain categories of errors, compilers can.