The secret as stated is the comlexity of a JIT. In practice, that dynamism just isn't used much in practice and in particular in optimization targets. The JIT analyses the code paths, sees that no writes to the target are possible so treats it as a constant.

Java has similar levels of dynamism-with invokedynamic especially, but already with dynamic dispatch-in practice the JIT monomorphises to a single class even though by default classes default to non-final in Java and there may even be multiple implementations known to the JVM when it monomorphises. Such is the strength of the knowledge that a JIT has compared to a local compiler.