I thought I would just share some perspective.......The debate between hardness and toughness is very old and very controversial/contentious. The debate between a "carbon knife" and "stainless knife" is equally similar. However, if one takes the time to understand what this actually means then the debate becomes more about science and design. The fundamentals of knife engineering start at the molecular level and how the molecule bond at the atomic level. Each type of steel has different properties because of the unique make up of specific steels composition. However, this is not everything, how a knife steel is "developed" (ie manipulating it at the molecular level) into a usable knife is a huge factor.
When it comes to mass production one doesn't need to have anything fancy to make a quality knife, however, starting with a good knife steel, properly treating it with a designed heat treat for that steel will yield a very nice knife. I will note that lower priced knifes usually have a lower hardness (usually around 56-57) because it is ideal for the steel they are made from, it is easily manufactured, and it usually has high toughness (but not always). This comes at a sacrifice because the molecular bonds might not be optimized and it could bend (yeild, ie fail) more easily, and require more frequent sharpening however, these hold a reasonable edge, sharpen easy and usually make a good knife.
Typically higher end knifes ie for example the 4-Star Henckels I happen to have on my counter top (some of the set are from 29+ years ago) spend a little more time in the manufacturing process to get a more optimum balance between hardness and toughness. This includes a cryo treatment to maximize the hardness without sacrificing the toughness (harness usually around 58-59). These can be very nice knives, but they require more effort to sharpen, and they will break before they bend (bending and breaking are both failure though). The trade off is they hold an edge longer and tend to be better with corrosion because the molecules at the molecular level are "tighter" spaced.
Mono Steel vs Damacus (a combo steel) is also a debate but if one understands the molecular bond in a knife steel a Damacus steel "can" be equally strong and in some cases (if properly design and executed) have some enhanced properties over a mono steel. A true san mai for example. A true san mai has a hardenable center core with a non hardenable surface. The blend of steel has a composite molecular blend to optimize the internal moment stresses when a knife bends, ie the bonds on the surface where the molecular movement is highest and under the most strain have a more flexible non-yielding composition which "protects" the stiffer edge holding core (the centered core has less internal moment stresses).
Many custom knifes strive to reach a balance of toughness while reaching a hardness above 60. There are many steels and "procedures" to result in just that. For example, a disposable razor has a stainless steel that is similar to AEB-L stainless, and that little flexible razor blade is usually at a hardness of 60-61...its amazing how they flex but yet cut....but they are design to do just that. I happen to have a kitchen knife sitting on my desk that is out of AEB-L stainless that has a tested harness of 61 that I have dropped tip first on the garage concrete (didn't do it on purpose!!) and it didn't break or bend or even make a mark in the 0.015" tip. It will take some skill to sharpen but will hold an edge for a very long time.
What is true and undebated and will be forever strived for is the "perfect knife steel" and this includes the debate between a $$$$ and a $ knife. I happen to have many versions of the $$$$ to the $ knifes in my kitchen and they all perform as they are designed to. I do know that the $$$$ 4-Stars were worth every penny or should I say 0.00228 cents a day for what I paid for my chef knife more than 29 years ago.
Just a final thought. Putting a steel in a dishwasher and subjecting it to 145 - 165 degree degreaser infused water will remove the oils from the surface of the knife and "find" any and "all" imperfections at the molecular level (which exist on all steels) and will accelerate the breakdown of these molecular bonds. IE dishwasher safe doesn't mean dishwasher proof!
PS, I sharpen almost all my knifes with sandpaper and most professionals do as well. It just happens to be in a belt form. IE the sandpaper on a PVC is very very very effective if you change out the paper offten!