There is no religion in WOT. There is a general sense from the individuals in the WOT world that there is a sentient (although there is no proof of actual sentience) being who created them. There is also an "evil" force that clearly has sentience. None of is means there is an actual deity. The Dark One might wish to become a deity, but more likely seems to be a nihilist.
Let us unpack this: you think there's a chance the Creator isn't real. Within WoT, though, absolutely no one argues that the Creator isn't a sentient deity who created everything. Lets say you're right. By that logic, can an atheist in our world say: I believe God doesn't exist. Yes, Christians and Hindus and Muslims do, but since I'm right, Christianity, Hinduism, Islam, etc. are not religions?
I think religions are fundamentally defined by the belief of its followers. Christians believe a set of tenets and stories. They're almost certainly not real, but that doesn't take away the fact that Christianity is a religion.
Similarly, even IF the Creator is merely a myth/legend, the unified belief of everyone in the existence of the Creator makes it clear there IS religion in WoT. It just has no organization, lacks a priestly class, and generally tends to have no precepts on human behavior.
Possibly, but that doesn't quite explain the Voice that spoke to Rand on two instances.
He was, in early drafts of EotW, but this is just not true in the main series. Rand faced him in aMoL, and the Dark One is clearly an entity not some human with immense power. Rand literally holds all of the Dark One in his "hands". Kinda makes it hard to say he was still deluded and believing in myths.
I think the idea is that anyone familiar with Manichean religions would be very comfortable with the "how". The Creator and the Dark One precede Creation. They are elemental forces with sentience. As such, "how did they come to be" has no answer, just as there isn't one in other religions which have such deities.
So by this logic, since no one doubts Zoroastrianism is a religion (one still practiced in India, btw), there IS a religion in WoT, right? Only, it is far more widespread.
Sorry, but Lanfear, at least, seems to believe in the Creator. Further, the Second Agers spoke most of the Prophesies of the Dragon, which certainly mention the Creator.
And there's this, from Rand's visions in the Waste:
Dark-eyed Deindre faced her with a more usual calm. “I am not the Creator. I can only tell you what I Foretell.”
Further, several glossaries mention the Creator and the Dark One, and they are always referred to as actual deities, the sources of good and evil, and of the One and True Powers. I fail to see any evidence that RJ wanted us to question the existence of either as a real deity. And whether he did or not doesn't have much bearing on whether there is any religion in WoT.