My point isn’t about them needing the Sunwell to cast spells that need sacred magic, but about the fact that worshipping the Light has never been part of High Elven society. I’m talking about faith, not magical abilities. So far I have reread bits of the Chronicles about the High Elves since their departure from Kalimdor and there is no mention of them or their priests having any sort of revelation about the Light. What characterizes priests among all the races who can play that class is their faith in something, whether it actually channels sacred Light magic or not. If the Sunwell, the only thing Quel’thalas Elves have faith in, did not contain sacred Light magic before the end of TBC then their presumed faith in the Light can’t be affirmed. The fact that this idea is mentioned nowhere outside of « Blood of the Highborne », short story that was supposed to be about Kael’thas and has changed authors multiple times, is disturbing in my opinion.
What could be true, but has yet to be confirmed, is that the Light can be worshipped and channeled through the Sun, the same way the Tauren do it with An’she - but it doesn’t really work, because the Arakkoa worship the Sun and Sun magic seems to be a separate thing. Although the Quel’dorei named their capital city Silvermoon, they made a point of replacing the moon with the sun in their tradition, not with the Light which is, at the end of the day, truly worshipped by three races so far: the Draenei, humans and dwarves. All the other races that have priests do not believe in the Naaru and I count Blood Elves (before the end of TBC) among them.
I just made a new Blood Elf priest on Classic to see if there is any direct mention of the Light in the quest lines of that class, I’ll post them if there are any.
I don’t see why they couldn’t, absorbing the mana of many wyrms makes it possible.