Berowin directly says in her quote that her secret is practice. She's probably good with Spirit but she's clearly a woman who has spent decades playing with this weave and making it more efficient. It's possible that many different shields are possible. I don't think anyone, including the Forsaken, have taken the time to practice shielding to that degree but they do perhaps know of ways to weave stronger lattices that exceed Aes Sedai shields. We know from Elayne that practicing with Air made her very powerful with it, and Leane/Suian learned to work more efficiently with less saidar. Demandred said that he's had so much time to study war and dueling that no mortal man can match him, so there's a general theme of practice making perfect. It likely extends to the Power too.

Berowin probably found something new... A soft shield that bends. I suspect the standard weave is like a net made of rope and that perhaps some AOL individuals know how to weave shields made of metal wire. This is why Osan'gar says he can get around any shield.... The knot is where the flaw lies.

I think your theory is original and explains many shielding dilemmas in the series.