Yeah, I rather see the events at the Eye as a momenteous step in Rand's path (comparable to the taking of Callandor, to his trip in the Rhuidean columns and a series of such events) that will eventually lead him to SG, but I don't see it as much of a quantifiable and undebatable victory for the Light as such. It's more like the first stalemate between Shadow and Light, and Ishamael probably expected all along he wouldn't succeed that fast at his first attempt - even his Dark Prophecies seem to say he wouldn't (However, I think the Dark Prophecies are counterparts to those originating from the Pattern, and contradict them - they are what will happen if the Shadow manage to derail the course of the Pattern, Ishamael must have seen some of those coming true or he wouldn't place no faith at all in them),. He's looking for nexus in the Pattern when he thinks he can make the Pattern go off course and thus derail the prophecies (he may well be right this is the Shadow's main chance - if the Wheel manages to keep things on track, the Shadow will fail in this Age), but in TGH Ba'alzamon talks to his followers as if failure wasn't such a big issue, because there's plenty of other such opportunities down the line. He followed a similar vision in his discussion with Rand in TGS. He would rather win now, and so would his Master, but Moridin is or think he is eternally the Champion of the DO and if they fail in this Age, there will be more opportunities in future turnings and eventually they'll win. I think the Shadow recovered way too fast from the events at the Eye for this to really count as "a big blow" and there's still the fact the whole event is ambiguous as we don't know if Rand emptying the Eye negated something else he could have used the Eye for and that the Shadow feared more. We know Ishamael engineered Rand's coming to the Eye - at least he planted all the seeds, and it seems the last of those was telling Aginor about it or otherwise attract his attention to this pool of saidin in some way, knowing Aginor wouldn't resist desiring to use the Eye, and thus he would use the boys to get there and place them where Ishamael wanted them to go. At leaat, it's what Ishamael pretended he wished to happen - if he said that to save face, we'll never know.. but his engineered manipulations of Farstrider suggests he was telling the truth.

If anything, the biggest blow to the Shadow in TEOTW - one they didn't see coming - might rather be the event that set everything in motion and ruined Ishamael's opening moves: Moiraine's timely arrival to the Two Rivers, bringing the Wheel's set of main players together (herself without whom Rand's cause is apparently hopeless, Egwene who would be the "TG Amyrlin" that would undo the Shadow's plans there, Nynaeve who would pair with Rand to cleanse saidin, the all-important three boys and even Lan and Thom), and introducing briefly the main players who would eventually join this "main cast" surrounding the ta'veren, like Min and Elaynen whose ties to Rand and their love for him would play a vital role in making his final epiphany happen. Without Moiraine's arrival and escape with the boys and Egwene, Ishamael had the three boys to play with freely.

Another event that might constitute a much bigger "blow" to the Shadow in TEOTW could very well be Fain's possession by Mordeth's soul. And I think we don't fully understand as of yet the full purpose of having marked Mat with the taint of Mashadar. I think it may be linked to the final and real purpose of Fain in the endgame. Why and how I don't know, but I think we have a missing link there, like we don't understand the real purpose of the Wheel in Perrin's connection to the wolves.

But well... in the end there's just Rand's epiphany and the Cleansing of Saidin that are very obviously huge blows to the Shadow. I think we're very likely missing the real meaning of other events at this point to find a third event that really stand out. There's so many other events that played their part in placing the right people in the right place, hurting the Shadow's plans that it's near impossible to determine which one counts more than another. For example, the kidnapping of Tuon and Semirhage's capture largely put an end to centuries of efforts to manipulate the Seanchan for the Shadow's purpose and, it appears, prevent them from playing their true prophecized role in the Last Battle. But none of those events seem to be in the same league as the Cleansing and Epiphany. My guess is that for one or more events in that league, we have to wait for AMOL.