Daedric and Ebony are more or less the same substance, you said it yourself and are both abundant in areas with lots of lava. Thus it more likely than not forms in a similar manner to ebony. It's certainly the more probable answer than anything you can actually provide to the contrary.
If you can find a better (and by that I mean more likely and more plausible) reason why there's so little ebony outside Red Mountain and the Deadlands, and so much in those areas, feel free to come up with one. And saying it's god's blood won't work, because that's not mutually exclusive with being an igneous substance.
Lava is everywhere in the Deadlands. And again, I find it more likely than not that if ebony is found near lava, then the very similar substance that the Dremora have is also found near lava. Not conclusive, but again more likely than not.
It's a theory, there's always a little room for doubt. If you can actually come up with an opposing theory that not only takes all the facts we know into account, and remains probable and plausible, feel free to tell me.
I'm not debating the conclusion that "Ebony is a material formed from cooled lava". Actually I'm trying to come up with a reasoning that supports that conclusion. Yet I'm having a little trouble doing this from the facts you provided.
You use the word "Daedric" in a sense that seems to imply "Daedric ore". Yet Daedric ore is not a known concept in lore.
I assume that Daedric Armor is made from Ebony. You seem to assume the same you've said in your proof that: "the abundance of it in the hands of the Dremora, the abundance of it in Red Mountain" The only relevant abundance in red mountain is ebony. Hence fact 2: Ebony is abundant in the Deathlands.
You agree that fact 2 is correct, no?
It's also important to realize that correlation is not causation. The co-occurrence of two events does not say anything about the cause of either event. They might co-occur because of a third event which always causes both events. As such their correlation doesn't say anything about the likelihood of "Ebony being a material formed from cooled lava". It does suggest though that when you do find lava, you have a good chance at finding raw ebony.
Yet we don't even have such a correlation. What I'd say is missing from the argument is the observation that raw ebony is found in places where lava is or once was in the Deathlands. Then we could say that raw ebony is (nearly) always found near lava so it might be cooled lava. Currently the only ebony found in the Deathlands is generally found in processed form near or on dead Dremora. Basically you need to find an ebony mine in the Deathlands.
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Also I've updated the argument to reflect more percicely that Daedric Armor is abundant in the dealands, and that thus Daedric ore must be in abundance in the Deadlands. I've also added the fact that Ebony is also found in places where there is no Lava.
Goal:
P) Ebony is a material formed from cooled lava.
Facts:
1. Ebony is abundant on Vvardenfell
2a. Daedric Armor is abundant in the Deadlands.
2b. Daedric Armor is made from raw ebony.
2. (2a& 2b) Ebony is abundant in the Deathlands.
3. Lava is abundant on Vvarndefll.
4. Lava is abundant in the Deathlands.
5. Ebony is found in places where lava is or once was on Vvardenfell.
6. There is no Ebony in the Shivering Isles.
7. There is no Lava in the Shivering Isles.
8. Ebony is found in places where there is no lava.
Reasoning:
8. Because of 3 & 4 we can say that Vvardenfell and the Deathlands are geologically similar.
9. Because of 3 & 7 we can say that Vvardenfell and the Shivering Isles are geologically different.
10. Because of 4 & 7 we can say that Deathlands and the Shivering Isles are geologically different.
11. Because of 1 & 2 we can say that the Deathlands and Vvardenfell have similar amounts of Ebony.
12. Because of 8 & 9 we can sya that Vvarndefell and the Deathlands are geologically different from the Shivering Isles.
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