Have you ever heard this one before?
"Why should I take the Christian God seriously? There are plenty of other gods and religions around, and you don't take them seriously. I don't believe in Yahweh for the same reason you don't believe in Ra or Zeus or Mithras."
This one's a stock argument from the ranks of the so-called "New Atheists." Some might find it convincing. I just find it vexing. It's a common misconception, borne out of a now-unremarkable ignorance of history.
There is no comparison between Jupiter and Jehovah. That's not because the one is true and the other false. It's because there, literally, is no comparison.
Polytheism is not a form of theism at all.
If you're looking for proof, looking at the genealogies of the gods. Zeus, "father of the gods," was the son of Kronos and Rhea. Kronos, "king of the Titans," was the son of Ouranos and Gaia: that is, he was the son of "Father Sky" and "Mother Earth."
The Greek gods exist within nature. They are, in fact, the naturally-born children of Nature. Nor is this the exception, for this is true of every other mythology with which I am familiar -- Roman, Egyptian, Norse, and to a lesser extent Sumerian and Hindu.
The gods did not transcend Nature, but were part of it. They were not creators, but creatures like us. They were merely more powerful than we were. When the pagans offered them sacrifices, they were not being religious, but political. They sacrificed to the gods for the same reason they sent tribute to powerful neighbors: they didn't want to be crushed to a pulp.
This is the fundamental divide between polytheism and monotheism. Indeed, polytheism is largely silent on what we would consider theological questions. If pressed, pagan mythology is pretty divided on many of these issues. Some of the Greek myths indicate that Gaia (i.e., Nature) was eternally pre-existent, while Hesiod's Theogony states that Gaia and the other protogenoi (i.e., primal gods) were born out of a pre-existent Chaos.
Where the Greek 'theology' might be classified as pantheist or even materialist, Hindu doctrine is henotheistic, or even a kind of monotheistic pluralism. Certain passages of the Hindu Bhagavad Gita speak of Krishna as the avatar (that is, incarnation) of the One God who transcends nature and all creation. It is for this reason that many Hindus worship Krishna as Svayam Bhagavan (the "Lord Himself"). It is for the same reason that Hindu religious practice is typically henotheistic: practitioners focus their worship on a single god as the primary avatar of Svayam Bhagavan. While they may recognize other gods in the pantheon, those other gods are considered as secondary or subsidiary avatars of the One God's true nature.
Let's return to the original point. There is no comparison between Jupiter and Jehovah, nor between monotheism and polytheism generally. The polytheistic gods were not supernatural beings of power; they were natural beings with superpowers. The nearest modern-day relative of the pagan gods would not be the God of Abraham; it would be Clark Kent.
We should speak of the Greek pantheon in the same sense that we speak of the Justice League of America or the Avengers Initiative.
One final note on Hinduism: there may be no comparison between Jupiter and Jehovah, but there does seem to be a direct comparison between Krishna and Christ. At the very least, they both speak of (and claim to speak on behalf of) a single God who exists over and prior to the created order. This was one of the reasons for C.S. Lewis' sweeping claim in Surprised by Joy. Having dispensed with atheism, C.S. Lewis reviewed all of the theistic traditions, and found that he could narrow his choices down to two: Christianity and Hinduism. These two were the only viable faith traditions, for only these traditions were actually theistic.