I think in many ways Darius is right about this. I'd like to raise a few points.

Firstly, channelers can use the power that drives the universe and most of them know it, even if only on a subconscious level. What's worse is that they are living in a feudal and not very advanced society, and human nature naturally gravitates towards "boldness", arrogance and similar traits especially when one is handed great power (and longevity). Some of the stronger channelers have been said to be able to tear down half a palace if they want to. There are very few truly humble channelers in the books, and we've seen channelers fall back on the True Source if they don't get what they want. Channeling is a lot like physical strength - powerful, athletic and good looking people are often arrogant and "bold". It's a theme as old as civilization. Anaiya's statement isn't absurd if you consider that the Power is what has established the hierarchy of the WT. Right or wrong, there is no evidence that this has changed. They mentioned it when they chose Egwene as the rebel Amyrlin, and it has been the reason that they have hounded Cadsuane to be the Amyrlin several times, even at the very end of the series. Cadsuane mentioned that she was very arrogant in her power when she gained the shawl, until she was humbled by a near toothless wilder. She is almost the only character whom I can think of who appreciates that even the greatest can be humbled. Most other characters think that they were unlucky and will 'have their revenge'.

One should also remember that half of the AOL Aes Sedai joined the Shadow during the War of Power. Channeling definitely gives people a sense of god-like power in most instances, even if it's not fully apparent at first. Rand's allusion to Moiraine as a 'little sister' is more than a hint that this sort of structuring may have been present then too.

The actual act of channeling even creates euphoria, and Nynaeve under Compulsion admitted that having access to so much power terrifies her. It's very likely that boldness in personality grows with strength in the Power, especially in the WT where people have to respect you if you're strong even if you're an imbecile (look at Elaida). I'm not saying that it's intrinsic, but rather that it is reinforced socially. Aes Sedai are told they are better than non Aes Sedai, strong channelers can boss weaker ones around etc. There are countless times when AS have told Nynaeve about how massive she is going to be one day and after a few years that has got to rub off.

Secondly, no one has introduced anything about relativism. Many of the Forsaken are akin to AOL royalty. Most of them were world famous whereas Mesaana was not. I don't think it's an easy crowd to be around unless you have very good self-esteem. Mesaana was not an achiever in her age, and she's not even beautiful (sometimes this is enough for even a modern woman to make her feel diminished). Same with Moghedien. Compare this to the others who are all very strong, beautiful and formally accomplished and it explains a lot. Rahvin may not be famous, but he's pretty much as handsome as a man can be and as strong in the Power as possible - I doubt he's had to face many serious social issues in his life that he couldn't get past. Of course, when Mesaana is around anyone who is not Forsaken (like Alviarin), she comes across as great as any queen, and there's no lack of 'boldness' there. Her massive arrogance around Egwene was not subtle at all. There are many other examples - Nynaeve is a very bold woman, but she becomes meek around Alivia. Daigian sits quietly among other Aes Sedai because of her weakness, yet that meekness vanishes when she's with her warder or is out and about like as an individual Aes Sedai.

As a last point, I also don't think Mesaana has a capacity for evil that many of the Forsaken have. She basically admits it when comparing herself to Semirhage. People like Graendal, Lanfear, Demandred, Aginor and Ishamael have almost inhuman capacities for evil. It's unlikely that all of the Forsaken have the same capacity for evil. Many merely wanted immortality, and Mesaana was more obsessed with her Nazi children's courts from a distance, than someone like Semirhage who was trying to keep people alive for years in agony, Lanfear driving people to suicide in dreams, or Demandred feeding whole cities to Trollocs. It's likely some of the Forsaken often thought "what the hell am I doing here?"

I'm not surprised that Darius thought that Mesaana should be less than 2. I have never seen Mesaana so high on any strength list over all the years that we have been fighting about it. It's likely that she's like Aginor - very strong but not very charismatic.