For the obvious reasons that so many channelers die of natural causes and etc that it's rare for an overall reflection of what an 'average' is is very difficult to achieve.

For example, we don't know if being average in strength is synonymous with having this strength level occur more frequently in a given population; we know that many of the women who come to the Tower are quite weak, but they represent a subset of the overall population. I think it is impossible to extrapolate from that.

I'd also say it is impossible for us to really figure out effectiveness from looking at our virtual numbers and RJ's most likely 21 level list - I say this because Asmodean, for being an unremarkable Forsaken, actually seemed very dextruos and in many ways possessed of more dexterity than the more powerful males during his battle with Rand. It's actually strange to me how often this is the case in the series, but effectiveness doesn't really seem to go hand in hand with strength in the Power; it is often the stronger channelers who rely on brute strength while the weaker channelers demonstrate the most mastery. I like the attempt you made to quantify this, though, but I think it would drive you insane to try to calculate Aviendha's comparable strength to Rand using the half-mile long furrow in the ground her fireball burnt.

I'm of the honest opinion that RJ didn't have a clear system in this regards in the same way other writers have: one of my critiques is that he often gives the appearance of having detail and complexity, but when you review his writing and passages from the story, it's all a meandering collection of generalized statements. He wanted maximum freedom as a writer, and often he did this by attaching caveats to any informational detail a reader could use to figure out a large-scale truth. You can't extrapolate anything from the size of Aviendha's gateways, for example, because there are at least two factors that make exceptions to the general "size of gateway indicates overall strength".

I'd almost say that it is as simple as "Rand is much stronger than the average channeler by an unknown order of magnitude neutralized somewhat by the possibility that he could be killed by a crossbow bolt to his back" and leave it at that