A Quick Objection to the Modal Ontological Argument

(From an old Facebook post of mine back in 2018)
Assume Platonism about properties, propositions, and possible worlds. Such is the natural backdrop of the modal ontological argument. Assume further that the key possibility premise of the modal ontological argument is true, viz., that there is a possible world at which maximal excellence is exemplified. Then by Axiom S5 and that premise, we get the God of classical theism -- or do we? Seems to me we don't. For the picture is that God is ontologically posterior to and dependent upon the existence and ontological structure of the platonic multiverse -- God's existence is the ontological consequence of the nature and structure of platonic space. But if that's right, then God is, in a real sense, a dependent being, in which case classical theism is false.