I think Sanderson misspoke when he said that Cyndane is very much weakened. This doesn't make sense based on information from the books. For example, Cyndane matches Alivia while Alivia has an angreal. Although this passage has sparked debate over who would be stronger if Alivia didn't have the angreal, most interpretations lean toward the idea that Cyndane is stronger than Alivia in the One Power. RJ said that Cyndane matched the stronger Alivia because she was a more skilled channeler, but if Alivia is so much stronger than Cyndane, as your list seems to imply, and had an angreal, no amount of skill could make up for such a massive difference in strength.

Also, we know that Cyndane is stronger than Graendal. From comparisons at Forsaken meetings and the opinions of other Forsaken, I have a hard time imagining Graendal to be weaker than Semirhage, although Semirhage and Nynaeve may very well be on the same level at this point in the series. I agree that Mesaana is weaker than Semirhage, and Moghedien is of course the weakest of the bunch. I would organize the Forsaken strength list as follows:

Lanfear
Cyndane
Graendal
Semirhage
Mesaana
Moghedien

The only interesting information Sanderson has given us regarding comparative strengths is the current strength of Nynaeve. I still think the traditional interpretation of Forsaken strength levels is valid, and has two decades of quotes from the books to support it rather than just a comment from a tired author at a book signing finishing a complicated series that is not his own.