I wrote about that (and the drawbacks and alternative takes) here: https://news.ycombinator.com/item?id=16540223 but yes, in a nutshell, "move the problem from dom-diffing to map-diffing" is basically what a reactive system is supposed to be taking care of.

You're absolutely right that reactive systems are not trivial to implement (let alone implement well), but inefficient DOM recreation under these systems is a symptom of poor granularity in the reactive layer (which may be a problem with the reactivity library just as well as it could be poor usage of its API), rather than a limitation of the rendering library itself.