In regards to ATS34's toughness, the real question is, "compared to what?" At a relatively high hardness, it is still tough enough to be a reasonable choice for many uses. On the other hand, it's not the best choice for a host of other uses.
ATS-34 is used and heat treated by so many people, the performance range seems to vary widely. Even within a single maker, heat treat recipes seem to change. For example, Benchmade for years had the rap of putting out very hard -- and thus brittle -- ATS-34. And sure enough, I've seen my older Benchmade's chip when I didn't expect chipping. On the other hand, my Axis is sharpened to 15-degrees per side, and takes everything I can throw at it. I've heard other people get similarly good results with newer Benchmades, so maybe they've backed off on the hardness or improved the heat treat process.
I definitely need to update the Steel FAQ. A few years ago, ATS-34 was the best (or rather, the only well-known) choice when you wanted to go stainless, and leave the steel really hard. These days, there are other choices, staom;ess steels that can get just as hard and hold an edge as long or longer, but are as tough or tougher.
Joe