Much agreed. My old 1MZ-FE and my almost as old 1NZ-FE are good examples. They are very different engines in terms of what they do to the oil. I typically run about 10K on the ECHO and when I had the valve cover off at around 300k it looked very good inside, much like the Sienna did at less than half that mileage on the front cylinder bank. Conversely I would never, ever run 10k on the Sienna regardless of the oil.Is that unique to Toyota or all engines? Is it a bad design or are the 10K OCIs causing wear? Are the oil filters premium or rock catchers? Are the engines DI or MPI? What oils were used in those engines? Were the air filters maintained?
Plenty of vehicles that run 10K OCIs and do not have issues. I had a 2010 FX4 with a 5.4L in it that starting at 100K miles I ran 10K-17K OCIs and it saw heavy towing for 45% of the 160K miles that I put on it. Zero oil consumption between OCIs.
I do not think you can make a general statement that "something that happens to the oil between 5k and 10k where it shears/get dirtier/additive package gets weaker, etc" and have it universally apply to every engine--far too many of them with 10K OCIs for far too many years for that to be true.