Maybe that's the goal of a compiler (though I'm not sure I agree), but that, to me, is somewhat subservient to language design and expressivity.
You can't really dismiss a language feature because an imagined implementation of the compiler would cause lots of small allocations. Just as one concrete example, Python has a special pool of tuples to optimize the case of iterating over key/value pairs in a dictionary (and likely only one tuple is used per for loop). Java does something similar-ish by relying on an Eden space in its generational garbage collector.
In Javascript, if it were the case small delimiter objects were used for promises and they proved to be a performance problem, I can imagine a couple of ways the interpreter could optimize that object out.
You can't really dismiss a language feature because an imagined implementation of the compiler would cause lots of small allocations. Just as one concrete example, Python has a special pool of tuples to optimize the case of iterating over key/value pairs in a dictionary (and likely only one tuple is used per for loop). Java does something similar-ish by relying on an Eden space in its generational garbage collector.
In Javascript, if it were the case small delimiter objects were used for promises and they proved to be a performance problem, I can imagine a couple of ways the interpreter could optimize that object out.