And that is your prerogative.
And in an ideal world you are correct, everything should be equal, this is not an ideal world.
As you say iso makes up one third of the exposure triangle, when was the last time you had your shutter adjusted or even tested? Back in the day we had to send our cameras in for CLA's pretty much annually, that would be a clean, lubricate, and adjust. The adjust part would be shutter timing, so does your shutter expose for 1/1127 sec or 1/963 sec when it is set to 1/1000? Your apertures, are they exactly where they should be, probably not as they rarely are, not to mention vignetting and the huge exposure variations that can induce. This is part of the reason top level cameras allow you to adjust for these metering differences.
So built into our exposure triangle are manufacturing tolerances for aperture and shutter speed, and the ISO allowable "rounding" for iso values, add in the confusion between 18% grey, you know the value everybody assumes is metered middle grey, and the fact that Canon meters (along with many others) at 12-13% grey +/- meter manufacturing tolerances, plus the fact that focal lengths are normally only close to accurate at infinity and you can see why, after 30 years, I am fairly dismissive of doing things by the numbers.
The point to my first post was don't sweat the numbers, your histogram, along with a knowledgeable interpretation of it, is the most powerful tool you have for getting your exposure where you want it to be.
i agree completely. cheers.