They are looking for a way, not that a way has been found, I believe there was an interview once, where someone said that they might be a way in the future but as of yet, the original Ren’dorei is it (I will see if I can find it) For all we know they might be researching the effects of the Void on the Elves, what the long term implications are, or Telogrus itself, not to find a way to make new Ren’dorei, its just never stated (aside from NPC who talks about finding a way to replicate the process but not that they have)
I think we are going off extremely different levels of faith, think of my Ren’dorei as someone pointed out above, as a Sunday Catholic, she believed in the Light but it was a side thing, secondary to power (she is a Warlock as well, so power hungry with the purpose of protecting Quel’Thalas made sense for her). I think you are right that a Light Priest would make little sense as the two powers are diametrically opposed, the know thy enemy way could work, but studying the Darkhan and being exiled would definitely have given them pause, because it would have been so outside of what they actually believe and have faith in.