I find it beyond reason that the Forsaken use the exact same weave, or more to the point ONLY the exact same shielding weave as modern Aes Sedai. It's obvious that there are multiple ways to form weaves for pretty much any OP related feat, some more effective than others. Given that we've directly seen at least 3 occasions where a Forsaken clearly uses shielding to great effect over a stronger channeler (Lanfear v. Rand, Lanfear v. Asmodean and Graendal v. Aran'gar) it seems intuitively obvious that they are using techniques/weaves that are different from what Aes Sedai use.

I'm extrapolating from what we see from Berowyn's shield that flexibility in the shield is the key to this additional effectiveness, that does not mean that these shields are immediately flexible to the touch, only that they will bend rather than break when an appropriate amount of pressure is applied. In fact I'd say that I think if Nynaeve were to use Berowyn's weave against Berowyn we would not see the shield bend because Berowyn would not have the strength to apply the requisite pressure to force the shield. Perhaps Elayne or Egwene would be able to bend this shield but clearly they could not break through it. Perhaps if Nynaeve had used the same technique as Berowyn she could have held Logain with no problem, or perhaps this form of the weave is simply vastly more effective in blocking a woman from saidar and would be an epic failure in blocking saidin. It's not like Berowyn would have had tons of opportunity to practice shielding men. As I've said before, I suspect the existing weave the Aes Sedai use was probably used primarily to shield men and probably "perfected" by the Red, much like the Yellow "perfected" the Healing weaves all Aes Sedai used. After several thousand years it simply becomes part of the Aes Sedai standard set of weaves and no one thinks to tinker with it because they don't need too ... like so many Aes Sedai traditions they assume they've got the best solution and stubbornly refuse to attempt anything beyond.

Personally, I find it obvious that shielding men and shielding women would be more effective using different techniques. It's possible that Graendal used a totally different weave to cut off and shield Aran'gar than she used on Delana. Much like men use different weaves for Traveling than women use and the fact that there are many many weaves for Healing despite the fact that Aes Sedai only know and use the most basic rough forms.

So all of the quotes you keep throwing out are useless, because a shield is a shield until it comes across an unstoppable force. Think about a bow and arrow, the string on any given bow is obviously flexible, however the individual pulling it must be strong enough to draw the bow. To an individual too weak to move the bow the bow is essentially a solid object (thus Berowyn would be unable to bend Nynaeve's shield regardless of technique). To a person strong enough to draw the bow the string is a flexible piece of equipment, thus Nynaeve can and does bend Berowyn's shield. Just because something is described as a "wall" doesn't mean it's the same thing as something else described as a wall. Concrete and sheetrock can both be used to make walls, that doesn't mean they are the same quality.