That's quite the blanket statement. Refactoring is just as much of a problem in statically typechecked languages. I write unit tests for a large C++ codebase and find them incredibly valuable when refactoring. Typically each class has a responsibility. The unit tests verify they are carrying out that responsibility correctly. Acceptance tests validate behavior across multiple units (the hard stuff). I fail to see how unit testing in languages like C++ wastes time. We spend far less time finding and fixing bugs than when we didn't have them.

I've used a lot of languages, both statically and dynamically typed, and found unit testing to be very useful in both.

The idea that unit tests are not very useful in complex systems is very controversial and goes against established best practice in software engineering, the advice of pretty much every authority in the field and empirical studies.

Only testing hard stuff is only half the battle. Unit tests also test basic assumptions and have other benefits like documenting intent. See /Code Complete/ for evidence for the need for multiple angles of testing.