I agree with your theories in part OP. I actually think everyone is a spirit - or rather the divine spark that brings what looks like life is a part of the Fade (cf. how to cure tranquil). But I don't think non-elves were created. I think they're spirits too. I just think they all got stuck in what amounted to golems - like the dwarves.
In regards to a couple of quotes from Solas during his romance, he asks:
"What were you like before the anchor? Has it affected you? Changed you in anyway? Your mind, your morals, your... spirit?"
Before he said the word "spirit", he looks away, realizing what he was about to ask but finishes the sentence anyways. The other important quote he says if you chose "I don't want to lose you" then "I love you" as reactions to him leaving the poor Inquisitor behind:
Solas: "You have a rare and marvelous spirit. In another world-"
Lavellan: "Why not this one?"
Solas: "I can't. I'm sorry..."
If elves were indeed in some way part spirit or something related Cole, the theories about spirits and physical beings losing one or the other when the Veil was lifted could be likely. Maybe something akin to Flemeth who claimed that Mythal is a part of her and that a soul is not forced upon the unwilling.
"She is a part of me, no more separate than your heart from your chest."
This sort of makes me believe that in the epilogue (the one with both Flemythal and Solas), one doesn't actually take control of the whole mind, body and soul then goes "Oh hey! I just had a sex change! Woohoo! I always wondered what it was like to become an unwashed apostate hobo!" like I've noticed with some theories of who took over who. It's just like how Flemeth doesn't end up saying, "Mother! I'm so much taller. Is this what being a woman feels like? I feel bad for them, having heavy chests and all" after Kieran (Old God version) seemed to willingly pass on the soul to her. Though perhaps some small influence can act upon their actions like the dramatic change of Justice/Anders' views and solutions between DAO and DAII: from being:
"I escaped the Mage tower many, many times. It feels like a prison and has corrupt templars I want people to change that because it's not fair for us"
to
"MAKER'S BA**S, WHAT THE HECK IS WRONG WITH THIS WORLD? THE TEMPLARS WILL PAY WITH THEIR BLOOD BECAUSE THEY ARE ALL BAD AND I'LL BLOW UP THE CHANTRY AND NO, IT'S NOT IN THE NAME OF VENGENCE"
Then you have the Avvar and spirits merging (or something along those lines) with children in order to teach them things. Forgive me, I didn't play JoH. These things are so complicated but yet the truth might be so simple. The Inquisitor, or elvhen one at least, seems to have this "special" thing about them, and it is not the mark that caused this. I'm not sure if this applies to every race (save for the dwarves perhaps) or class having some lovely dovey or evil envy spirit/demon/ScaryGhostThingThatIsAPartOfYou. Or if it is just a very few, rare even, people that have this type of "spirit" fragment as a part of them regardless of race. Dwarves don't dream, meaning that something makes them resistant to its link, possibly in the blood: Surface-born or underground, dwarves are somehow like us when we get chicken pox but we're mostly resistant afterwards. What's weird is that Tranquil still dream, as Pharamond, once a Tranquil himself, from Asunder, explains:
Pharamond: "I realized early on that Tranquility wasn't repairable on this side of the Fade. It needed to be done from the other side. A spirit had to bridge that gap - and it could only do that if it knew exactly where to look. The Rite renders the Tranquil invisible to spirits."
Evangeline: "They're not just invisible, they're immune..."
Pharamond: "Not immune!" The elf became excited, in the manner of a scholar speaking on his favorite subject. "Undesirable! A demon looks to possess a man because it wishes to experience life. To them a Tranquil is no better than an inanimate object. Worse, since a Tranquil will resist. If it is going to cross that bridge to possess a Tranquil, it needs to be lured..."
Sounds like these demons are ones who wanted physical forms and can only do that by finding little unbroken bridges in the veil like possessing a mage or pressing against where the veil is thin like blood seeping out of a cut. If it is a possibility, most likely mages and elves could have some minor or dormant essence that acts as that "cut" for them connect to and channel energy from the Fade in some way or intensity. How large the "cut" is allows them to channel more energy. Though we do know that non-mage humans can dream too, but not as vividly and powerful as mages, maybe like a few pin pricks across the skin. Speaking of blood, don't Thedosians say that demons usually press against the veil in place where large incidents of death have a occurred such as battlefields? If so, it would be something like blood magic, for example, how the magisters opened the veil and entered physically with large quantities of blood magic, elf blood in particular according to a codex found in the Fade during Here Lies The Abyss. In another thread (or this one, I can't remember lol), some have speculated that Solas is amassing this herd of oblivious and possibly some non oblivious elves for a blood magic ritual to weaken and tear open the veil. There was more about why this would be an option and reasons to which Solas would do such a thing but I can't remember where.
I don't know but it's just a hunch