I know you can't AOT compile it away, that seems obvious, but what's the limitation that means you can't JIT compile it away? Like any other JS optimisation such as inline caching?
JIT compilation still involves a runtime performance penalty of the JIT compilation step itself, that has to be traded off against the runtime performance penalty of just running the Proxy logic without any runtime compilation step.
That's a nuanced tradeoff that has to be weighed on a case by case basis by various heuristics, and can reduce the runtime cost of proxies when applied to the right cases (and at the same time, could increase runtime cost if applied to the wrong ones: think overly aggressive inlining and its effects on memory usage), but either way it doesn't result in the Proxy abstraction becoming "compiled away" into something that has 0 runtime cost.