Hmm. It is obviously the scientific understanding of a rainbow yes, but, do you mean to say that God cannot use part of the natural weather/atmospheric tendency as symbolism? Life goes on for thousands of years as we know it, and God is mostly silent, but it’s foretold that He won’t be silent forever and many of us Christians are feeling the nearing of that era.
Of course God can do anything He wants. But I’m sure He can do better than an ordinary, garden-variety, happens-thousands-of-times-every-day somewhere standard rainbow.