If these dynamic languages are usually used in a mostly-static manner, just without the typing and some added load-time flexibility, doesn't that just mean they operate at a higher level of abstraction? Isn't that a good thing?
Your definition of good may or may not include "do these higher level abstractions preclude, in theory and practice, well-known and cheap optimizations?"
It would be cool if a language could be both, by using this research to create a language that recognises the difference between load time and run time. The dynamic parts would be used to load the program, after which dynamic changes would be turned off, allowing function dispatch or whatever it is that is slow in a dynamic language to be sped up.