There's another problem with trying to squeeze the "ancient elves" into being the elves Solas is concerned with restoring. Solas was going to throw down the Veil after the death of Corypheus, which he anticipated before he knew of or met any group of ancient elves that we know of - specifically the elves in the Temple of Mythal.
Inq: What would have happened if Corypheus had died and you'd recovered the orb?
Solas: I would have entered the Fade, using the mark you now bear. Then I would have torn down the Veil. As this world burned in the raw chaos, I would have restored the world of my time.. the world of the elves.
The world of the elves destruction is his responsibility. He feels this. It has an effect on the elves and that effect can only be embodied in the modern elves. They fit perfectly into the description of whom Solas wants to restore.
Inq: You were a hero, Solas.
Solas: I sought to set my people free from slavery to would-be gods. I broke the chains of all who wished to join me. The false gods called me Fen'Harel, and when they finally went too far, I formed the Veil and banished them forever. Thus I freed the elven people and, in so doing, destroyed their world.
Inq: How did creating the Veil destroy the world?
Solas: You saw the remains of Vir Dirthara. The library was intrinsically tied to the Fade, and the Veil destroyed it. There were countless other marvels, all dependent on the presence of the Fade, all destroyed. Your legends are half-right. We were immortal. It was not the arrival of humans that caused us to begin aging. It was me. The Veil took everything from the elves, even themselves.
What group fits this perfectly? The modern elves. Are they "his people"? In a very real sense, no. In a very real sense yes. They've had themselves taken from them. By who? Solas. Are modern elves aging and dying from old age? Yes.
But even if they've lost themselves, he still will try to restore them. This fits perfectly with his original plan, before they had to fight Corypheus.
Inq: That's the past. What about the future?
Solas: I lay in dark and dreaming sleep while countless wars and ages passed. I woke still weak a year before I joined you. My people fell for what I did to strike the Evanuris down, but still some hope remains for restoration. I will save the elven people. Even if it means this world must die.
So, even though he's mad at the Dalish and city elves for losing their way... Even though they've lost their identity and history... he still wants to restore them. He's responsible for their state.
The ancient elves at the Temple of Mythal haven't lost their lore and they haven't lost their agelessness. They still serve Mythal. Solas didn't know about them, thus his plan didn't include them. They aren't feeling the effects of the Veil like the rest of the elven people, since they have a magical Temple and uthenera to sustain them in their duty to Mythal. These aren't the elves Solas is talking about.
Now, that doesn't mean after he discovers them that he'd automatically spurn them joining his cause. Abelas very well may have joined up with him at some point. We don't know. There's no information available about that.