Every time a Zannah debate pops up, the same fallacious arguments tend to come up regarding Zannah's 'impenetrable' defensive prowess.
It's particularly ridiculous to claim that Zannah's defenses can't be broken even by a more skilled contemporary, unless their raw offensive power supersedes Bane's. In reality though, that really isn't how lightsaber duels tend to work. Out of everyone in the mythos, there wasn't a single duelist that could completely wipe the floor with Obi-Wan more consummately than Tyranus. And trust me, he did not have the ferocity of a Darth Maul nor could he replicate the brutal onslaught that Anakin could unleash. He overcame Kenobi's defenses through greater skill and bladework, and it's foolishness to think that the case is any different with Zannah. We saw from the second half of her battle with Bane that her technique could be effectively countered by greater technical proficiency, unorthodoxy, and precision. And it's silly to have thought otherwise in the first place. Soresu is a fighting form, not a durasteel wall.