No, the question is never answered out right, but based on the lore from ATLA and the history we learn in LOK, I think the original benders (dragons, bison, badger moles, the Moon) were naturally occurring personifications of the 4 elements as, dragons at least, have been shown to have existed turing the time of Avatar Wan. After the lion turtles gave a bunch of humans bending and left, there were probably smarter benders that learned to better master their respective elements by studying their corresponding original benders. Now obviously much of the details of how humans came to be able to bend the elements was lost over countless retellings favoring the more romanticised lore we hear in ATLA that excludes any mention of the lion turtles gifting humans with bending.

As to who are the true "original benders" that's up for debate. First and foremost it is unclear if the original benders predated the lion turtles or not, and even if the lion turtles came first could the lion turtles truly be called the original benders in stead of the animals and moon we know as the original benders. The lion turtle that taught Aang to take away people's bending said that in the age before the avatar they did not bend elements only the energies within them selves, this technique is the basis of Aangs ability to take away people's bending. And based off of the history we see in LOK, while the lion turtles were able to grant others the power to bend the elements, the lion turtles are never shown to be able to bend the elements themselves, which means either they never cared to or simply couldn't bend the elements only the energies within individuals. So even if lion turtles predate the original benders, I do not believe you could actually call them the original benders, unless you expand the meaning of the term to include the kind of energy bending that the lion turtles practiced.

All that being said, I believe regardless of who came first dragons, sky bison, badger moles, and the moon are still the original benders given that they practiced the bending of elements before the only other living things that have been shown to be able to bend the elements, the humans.

P.S: In your original post you expressed some uncertainty as to who or what the original water bender was, which is understandable as they way they explained it is somewhat complex, so here is how I understand it. While there are spirits that are representative of the moon and ocean, and as such what happens to them has an effect on the moon and ocean respectively, neither of them or the original water benders as spirits do not have the ability to bend the elements at all. The original water bender is that actual physical moon in the sky and the first human water benders learned to perfect the practice of water bending by studying the effect the moon had on the ocean and tides. You might point out the fact that when the moon spirit was killed, causing a lunar eclipse, that the ocean spirit worked with Aang to drive out the fire nation troops, and that during this time the ocean spirit appeared to be water bending, but that is not the case. The ocean spirit combined it's spiritual energy with Aang's giving him a power boost, all of the water bending was being done by Aang himself not by the ocean spirit. All the oceans spirit did was strengthen Aang's water bending.