Scala can work great in a large development team. Your sentiments about poor readability and maintenance have little to do with the technology itself; you could say this about any programming language.
People new to a technology have a tendency to flounder around a bit in the beginning because they're naive to common coding standards and principles. After those are found or established then Scala codebases are just as easy to collaborate with on than any other.
It is not mainly about conciseness. Conciseness by itself is not that important. Conciseness is a side-effect of being able to apply DRY and to build more powerful abstractions. You could write more concise Java by using one letter identifiers everywhere, but that would only make things worse, wouldn't it?
Scala may be good for one-dev company; but terrible in terms of readability and maintenance for a team where more than 3 programmers work on the same code.