No rebuttal here, but I'll attempt to validate my reasoning. So, Earwa>General Discussion is a very broad grouping, whereas the Series>Book>Topic format is, by its very nature, more specific, followed by the even more specific Atrocity Tales. I like to work from broad strokes down to fine details, and this structure fits that mechanic. Obviously, that's just my preference, so when I called it 'user-friendly' it was more about my user-friendliness, which is what was being asked initially (I think). So, just my biased opinion.
If we're more talking about logical order, then I agree with Madness. It absolutely should be the books first, followed by AT, followed by General.
I'm no student of the psychological effects of particular ways to present information, and getting the best benefit from that (i.e., user-friendly). Either way appeals to some part of my own personal logic mechanisms.
I'm as dissatisfied with my answer as I'm sure anyone who reads this is. Apologies.