This site has always been obsessed with power levels; it's amusing to see how many comments are on this post. I have never cared very much about power levels, and Dom said he never cared much either, but once we got our hands on the notes and saw all the detail on power rankings, making a list was just too tempting. So I guess the obsession rubbed off on me through Dom...
I didn't create this just to come up with the strength scale, I also wanted to look at how old some Aes Sedai were and their training times and nationality breakout etc ... Was a fun exercise to figure out who is Black Ajah and try and infer if strength level might play a role or if it was more heavily weighted toward specific nationalities etc ... Basically I wanted to look at as many data points as we have available cause I'm a nerd like that
I get it, and I did some of that on my half-assed spreadsheet. I wanted to do more but I had to do other stuff.
Some characters are more obsessed with strength than others. Considering the strengths RJ assigned to the Forsaken, it seems that they were kind of oddly not obsessed with strength. Most of the development of the Forsaken happened at a time when RJ hadn't really decided on their strengths, and I think it shows. (And not just in the BWB, where there was a half-assed effort to order the Forsaken by strength.)
The Aes Sedai hierarchy is based on strength, but then they have this weird custom where they're not supposed to talk about it, and RJ went so far as to have Eadyth say she felt the need to scrub her teeth after talking about it.
It was probably some time while RJ was writing books 5-7 that he felt the need to start making notes on Aes Sedai strengths. That would have been when he came up with the first system, with Elaida on top. Then somewhere between TPOD and COT he started using the new system. That's probably when he started trying to decide on Forsaken strengths.