Not quite. Our C++ code often does static_cast<> as a downcast based on testing some condition. That's a run-time type check. This isn't solely about those type checks that were implemented using some built-into-the-language type checking mechanism. Also, C++ does have a dynamic type check primitive (dynamic_cast).

We are mitigating these branch-based type checks with pointer poisoning, and I don't think that those changes are biased in favor of C++ or JS, since both are vulnerable.