This is from tFoH, in TAR. When Moghedien did land a shield on Nynaeve. As you can see, it is a wall.
Later in the same chapter:
Suddenly she was tying off the shield, the knot growing ever more intricate, until Liandrin lost the twists and turns completely. And still it went on. “There,” Moghedien said finally in tones of satisfaction. “You will search a very long time to find anyone who can unravel that. But you will have no opportunity to search."
The knot is intricate, but Liandrin never once says anything about the shield itself being different. She just calls it "the shield" as if she knows it, just like she mentions Flows of Air.
If there was anything special about Moghedien's shield, neither Nynaeve nor Liandrin mention it.
And look at this description from tSR:
Once again, nothing about the shield looks different to Nynaeve. You argue that maybe the difference is only obvious once the shield is in place, but 1)when it was placed later, Nynaeve calls it a wall and 2)Why would Moghedien need to use exactly as much strength as Nynaeve, then? If he shield is more flexible and different, more like Berowyn's, wouldn't it also take less of the OP. Instead, it is an exact match for Nynaeve's.
So the only evidence we have from an AoLer shielding an Aes Sedai is from Moghedien. And there is absolutely nothing different about her shield. Neither in how it is made, nor how it feels to women who are shielded. It certainly doesn't expand one bit for Nynaeve.
As for Lanfear's shield, it was different in that it allowed a tiny trickle of the OP, but she also makes it clear the pain thing is nothing special:
The tense she uses, and the "never" all point to the pain being a regular aspect of breaking a shield.
What evidence do you have that shielding was not a result of Aes Sedai searching for effective ways to stop males from destroying the world? We know Aes Sedai did a lot of research around how linking worked as part of stopping mad males, or at least controlling them. Given that Tower law requires a male to be brought to Tar Valon and put on trial, shielding would have been a massively important skill for early Reds to have mastered.
Wait, ou're claiming they forgot shielding and reinvented it in the 300 years after the Tower's founding? That is certainly not true:
This is before the White Tower was even completed.
You forget that the Breaking was also filled with groups of Aes Sedai hunting down the remnants of the Shadow, which certainly included women. There is absolutely no evidence that Shielding was a skill that was ever lost, during the Breaking. And it makes good sense that it wasn't. Shielding and Severing are major tools for any woman against both the Shadow and mad male channelers. They were probably among the weaves to survive the Breaking intact.