I'll try and be as thorough, yet simple as I can be here (based on my limited knowledge of metallurgy).
Carbon or Stainless, if you are below .8 percent carbon, then you will not form carbides, the iron will simply use up all the carbon. When you go above .8 carbon, you have excess carbon and can form carbides as well as different structures within the steel. This is why AEB-L is so fine grained. It has 13% chromium, but only .68 carbon, much below the .8 threshold, thus it does not form chromium carbides. The term "high-carbon" steel is "supposed" to refer to a knife with greater than .8 carbon, but I've seen makers often use it for steels with .6 carbon.
It is when we combine high-carbon with high-alloy (in this case 13% + chromium) that you will get big grain boundaries if the steel is not powdered or of utmost purity. If you stay below the .8 threshold you really don't need powdered metal if you have even decent temperature control. It's up to the heat treater to properly normalize and anneal the steel prior to heat treat. Powdered metals and inert atmospheres are 2 things we use today to produce fine grained high alloy steel. Some of these alloys allow for higher hardness and some of them even control grain growth to a degree, so yes, it is very much a balancing act, especially given the specific set of properties we are looking for to make knives with. The best that we can offer for better toughness and lower chromium are semi-stainless steels like the Kikuichi TKC and Konosuke HD steel. Semi-stain steel is some of the best all around steel for kitchen knives, many swear by it.
These high carbon alloys start to produce different types of grains when you start adding lots of alloys. It's the combination of alloys coupled with being powdered metal that makes a really great powdered metal. Adding Chromium in powdered metals greatly increases wear resistance and stain resistance. At low temps Chromium can actually control grain boundaries to a degree (one reason why 52100 is so great) but at higher levels and higher temps it will grow grain boundaries. Vanadium can combat grain growth problems but greatly increases wear resistance and temperature requirements. From what I gather, 2 of the best steels to balance most attributes on an exotic steel are s35vn and ELMAX. Both were actually developed specifically for cutlery, nearly an industry first. Like you stated before, very few steels are actually developed specifically for knives. These are supposed to have all the wear resistance but still be able to take to stropping well. Generally, the higher the alloy the harder to strop or put a very fine edge on, but pretty much all of the 3rd gen powdered metals will take a fine edge without much fuss. Some of the first gen powdered steels still suffered from losing their fine edge fast but that problem has pretty much gone away with newer alloys and finer grains.
About chromium and degradation: This is only partly true. Chromium can increase stiffness, making an edge less likely to roll meaning less honing throughout the day. However, this extra stiffness leads to brittleness, meaning the edge will break off faster than a carbon steel knife, leading to a knife that can't be honed back as many times or as fast as a carbon steel knife. It's the ease of sharpening, ease of honing, and extra toughness that makes carbon so attractive. If you don't have time to hone your knife, or are working with a lot of high-acidic foods, you will generally want a stainless knife over a carbon.
Did this answer your question? I apologize for any redundant information or stuff you may have already known, I always assume there's some first time reader's here. It's getting late and I'm a bit tired lol.