Fundamentally Nirn is a world where myths are real, but that's also meta-logic and not quite as satisfying.
Myths can be real, rather.
As an in world rationale you can see that the Altmer and Nords as well as other share the same stories about Lorkhan/Shor losing his heart -occasionally his heart is called 'the Divine Spark'. This includes the Yokudans who were culturally seperated from Tamriel until somewhere in the first Era.
The Yokudan example is a good one, but realistically if they were right, how would they have found out about it or come to the conclusion it was most likely?
This implies that these myths aren't simply made up stories to explain why the world is as it appears as most religions do, but rather the these myths are retelling of an actual event that everybody on Tamriel has witnessed.
There are similar elements between them, but distortions are also there by culture and stories retold once they've been reintroduced.
Now add into this that the 'alleged' Heart of Lorkhan actually looks like a giant Heart
I'm wondering why the shape would matter, but if the shape did matter it would mean Lorkhan was much more literal than he is generally taken. All those like him could be chipped and amputated to create strong weapons. Its a little cheap, but workable. It also brings the question if his heart functioned as a heart, how is it so tiny? Especially in comparison to the worlda around it?
and can be found in a crater/vulcano surrounded with Ebony which is also called gods blood
Circular logic. Myth reinforcing the myth, whether or not it is true. Even so, where is the armor made from Akatosh's blood?
(which infused with daedric souls gives you Daedric Armor),
Anything infused with daedric souls would or could become daedric couldn't it?
the myth that Lorkhans heart was ripped out and thrown across Nirn, splattering blood on impact isn't that far fetched.
It isn't far fetched, and it is the version I agree with, but it seemed there hadn't been a questioning of the accepted on the issue. A myth also said the heart was shot into the sea where no one would ever find it.
I think the red boiling lava is rather more obvious.
Heart of the world and world's blood.
Mixing metaphors, but it fits in a video-game sense.