You said that the Tower doesn't restrict women of higher strength. But the sample population of the Tower, ie. the thousand channelers we see, are skewed towards the center, with no one of very great strength or very great weakness. Which means Moiraine is not very far above the average of 50, and Egwene is clearly above it while Nynaeve and her ilk are far above it and closer to the upper end of the range.

It works really well if you make increments of 4.75. That gives us 21 levels, and you can place strong Aes Sedai like Anaiya or Myrelle or Sheriam at 50, and the list is quite good, in that case.

Edited to add... RJ never spoke of any relative strength scale. He said channeler strength is distributed over 21 levels, and that the channeling population follows a bell curve. Both statements refer to no mysterious relative scale.

The conclusion is rather inescapable... given the bell curve, a woman like Moiraine will have an effective strength greater than 50, but not much so.

And I'd like to know why this seems impossible. RJ made many comparisons between OP strength and actual strength. If you look at actual strength, the average man is likely to be half as strong as the strongest man. And that gap is still huge, still good enough to explain the great differences we see between the strongest and weakest channelers.