There is a greater opportunity, but it hasn't happened in practice. And even with Typescript's types, I doubt that it would make much of a difference because the type system is deliberately not sound and the types can't really be relied on. Typescript is a great way of reasoning about a program, but it's not meant as a runtime execution type system.

Yes. Another common example is that in languages without pointers, the lack of aliasing enables optimizations that are impossible for languages with pointers.

Also, C compilers generate efficient code by assuming undefined behavior cannot happen. (This sometimes corrupts buggy programs, because the type system can't guarantee undefined behavior isn't triggered.)

TS biases code to using objects of very consistent shapes, so the js runtime's assumption-based optimizations are deoptimized less frequently.