You are correct about the engine, more soot goes into the oil to reduce the particulates going out the exhaust. However, all engine oil had to meet CJ-4 specs including Delo 400. The same parent company may market several brands (i.e. Chevron/Texaco) but the formulations are likely different, additive package and treat rate. Also the additives may be from different suppliers. Engine oil formulations along with gear oil are VERY COMPLEX. Years of research and money goes into developing new formulations to meet the new specs. Another item that needs mentioning, the oil is developed in the lab running engine tests with "best guess" engine designs. And field testing of new oils is done in "older technology" engines. It is not until the engine OEs start producing the latest engines that one finds "downfalls" of the new lubricant (and that takes at least 500K miles). So 3-4 years after a new engine is introduced does one know the strengths/weaknesses of a lubricant. Same goes for gear oil. One of the biggest issues I had as a test engineer was getting "in bed" with engine OEs to evaluate new lubricants in new hardware before production. So likely the engine OE developed the new engine using "old technology" lubricants.