Well, the type system can be used to isolate side effects, thus ruling out large classes of concurrency bugs (especially with threads instead of separate proces

Well, the type system can be used to isolate side effects, thus ruling out large classes of concurrency bugs (especially with threads instead of separate processes or strict message passing (e.g. Erlang)). It can also prove that typing errors cannot occur, whereas with a dynamic language, it is possible for the program to be ill-typed in only certain circumstances (a function could return a different type depending on input). But yes, there are plenty of concurrency issues that are not greatly mitigated by static typing.