It's that. It's a continuous and linear scale, with each level covering an equal range. It's not stated black on white, but it's clear, notably when you see the life expectancy functions linearly, and that RJ made some comparisons by number of levels.

By the way, there was actually not a single mention in the notes Terez got at the library that the level system is more than RJ's meta-tool outside the fictional universe. Not once it's even hinted at that in the notes (or for that matter, the books) the White Tower uses a level system like this. I was a bit surprised that Harriet apparently decided it existed in the story. A lot of situations in the books seem to flagrantly contradict that (notably the numerous POV from sisters or even Forsaken that go out of their way to describe someone's strength by comparison rather than resorting to the scale, if it had existed. The vocabulary used to speak of strengths, whether by AS or AOLers, goes against that too. "As strong as a woman can be", "A sharp gap", "of not negligible strength" etc. It's all avoiding a formal scale, culturally . My guess is that they probably would have thought that vulgar/demeaning. No doubt there was a way to calculate precisely your strength, the way your calculate blood pressure, waistline, etc, but I don't think those numbers corresponded to "levels" nor that they were used by AS in daily life at all, in either age.

As for the WT, it's a strength gap that determines when deference/taking suggestions etc. begins. In the notes it said the gap starts at around 2 levels. The gap at which suggestions from a stronger sister become as good as orders is probably much larger than 2 levels (based on the way some of the stronger sisters tried to resist Cadsuane, I'd say it might as much as a gap of 6 to 8 levels)

In formal situations or when a definite hierarchy is required, sisters have ways to rank themselves, but in day-to-day situations, if falls back on personality, if the gap isn't large enough, and there's the other unwritten rule that a sister normally don't meddle in another's business.

I think the strength range covered by a level is larger than you imply when you say within a level they'd have to resort to duelling to decide exact strength. I think RJ was speaking of women who stood even closer than that in strength. RJ didn't need great precision (he would have assigned an exact strength to everyone, if he did), he invented that system largely to determine at a glance relationships betwen the AS, and eventually extended it, obviously to be able to keep track of the strength comparisons he was starting to include, and of certain details like gateways, etc. He devised the male levels, but by all evidence, he barely used the male scale at all in his notes.

I think he decided around the time of LOC (or before writing ACOS) to expand his original system (which I think covered only from the strength of Moiraine/Elaida at level 1 to what he saw then as the bottom level for the shawl at level 21). I think he likely started by subdividing his original scale to have a larger range of strengths for AS to use in Salidar or around Elaida, and with the Kin, the WF, the WO. This is when, indeed, strengths are really started to get discussed in the books.

I think this is when he built his "Aes Sedai bible", that is he created himself a bank of sisters, distributed roughly following his bell curve , assigned with an Ajah (to respect the proportions he had decided on), a level or range or levels, and occasionally other basic characteristics. He seems to have put a great deal of work into entering the new levels for women in his notes (the double system, we've surmised, was used to ensure no mistake and confusion between notes with the old system and notes with the new). Around the AS levels, he expanded the scale to cover all female strengths up to Lanfear, distributing the girls and the new stronger characters too, and he expanded it by the other end. My guess is that he set the last level at 66 to get 72 levels including the male ones, just because it was neat.

I think his notes assigning a strength to the male Forsaken (and the women) are from that time when he seemed somewhat enthusiastic about the new "complete" system. But it seems he never really bothered with it for the Asha'man, or extremely little. Male strengths are extremely rare in the notes.

Darius putting Morgase and Androl at level 66 is much too low (I think at level 66, a woman doesn't have the strength to do much at all with the OP, she just has the genetic abillity and can probably not be trained beyond touching the source, without involving an angreal, that is.

In a note relevant to Morgase's story, RJ said that below level 57, the ability to lift anything with the power (lifting stuff is a factor of comparison he used) drops to a feather. Morgase is at minimum 57, maybe a few levels above. She's very likely comparable to Sorilea. The difference is that Morgase doesn't have a personality that surrender control easily (like Nynaeve) and it would have been very hard for her to learn to grasp the source no matter what. As it was, her strength is way below the cut-off for the shawl, and even that to make Accepted. The AS awoke her ability for political motives, and I doubt they put that much effort into it when it was clear Morgase struggled. Sorilea, on the other hand, was taught as much as she could, and could perfectly embrace the Source at will and learn difficult weaves that she couldn't even make work. The WO understood that very weak women may not be able to channel much, but they still could pass on all their OP knowledge to their future pupils... I doubt the WO have lost weaves nearly as often as the WT did...

As for Androl, personally I suspect the last 6 levels aren't used for men. A level 60 man is comparable in what he can do with saidin to what a level 66 woman can.

My guess is that Androl is in the lower 50s or very high 40s.