But I understand that when you say you believe in a supreme god you believe in a supreme god.
Supreme to me is as you defined it.
Now, here you say “a supreme God” whereas before you said “the supreme God.” Do you see how that would make a difference? It would be the difference between my asking a Christian, “do you believe Jesus is the Son of God?” and asking, “do you believe Jesus is a Son of God?” That is precisely why I went to the trouble to define the ways in which I understood the word “the” to be applicable to this discussion.
Okay, then. I gave you options as to how I might or might not view Zeus as "the supreme God " depending on the way in which one intends that phrase. Which one is relevant to your actual question?
Yes, Zeus is the supreme God in my pantheon if we are using the first definition of supreme, as in the highest ranking, but not as in the highest in “quality,” whatever that might mean when applied to a God. This is not surprising as he is identified with the generative force without which nothing else exists or continues to exist.
No, I do not believe that Zeus is the ultimate God, as in rendering irrelevant all other Gods, either in the Hellenic pantheon or any other. I do not believe that He is or should be considered as the only God in existence or worthy of worship.
I think the root issue here is that polytheists adn monotheists have a very different understanding of what “God” means.
Let’s try this from another tack. Both the United States and Australia have Supreme Courts (though I believe in Australia the equivalent term is High Court for the one that covers the entire country), and those Courts have Chief Justices. Both courts are recognized as the highest legal authority in their respective countries and for the citizens of their countries. It is entirely possible that the High Court of Australia may make a judgement, binding upon its citizens, that is not in exact agreement with and may be diametrically opposed to the judgement of the US Supreme Court on the same issue. Because these courts are recognized as “the supreme court” in their own country, but neither as “the supreme court” for the entire world, this is not an issue.
The Australians are not bound by the judgements of the US Supreme Court and Americans are not bound by the judgements of the Australian Supreme Court. Nor are Australians required to believe that the US Supreme Court does not exist, is demonic, a fantasy or a "false court’ in order to believe that the Australian Supreme Court does exist and has power over Australian citizens (regardless of whether they personally
agree with the judgement made by the US Supreme Court

).
**For what? That Jupiter is the supreme god? Or, that Odin makes that claim as well?
I thought it was understood that in the various pantheons there is a deity that is held to be supreme. For Celts, Greco-Romans, Norse, etc.**
Yes, if by supreme one means highest ranking
within their own pantheons. I am still not sure that we are talking about apples and apples here, as Christians will also use the phrase “the supreme God” to refer to their own deity.
We can leave this until you can let me know if you mean by this question that Jupiter, Zeus, Odin and others are understood by their worshippers or that they claim to be “the supreme God” in the way that the God of the Hebrews and the Christians does. Based on your comment about exclusivity, I am inclined to think that you mean the latter.