Quite frankly, the supposed savings are rather nebulous when you consider a) fuel gauging errors b) fuel loaded by the bowser to the nearest 100kg c) assumed pax/cargo weights d) arbitrary diversion routings.
Don't forget that all those points you mention are constants: fuel gauges will always have errors wether you are a fuel saver or not. Neither can you change the bowser's fuel accuracy. What you CAN change is your fuel requirement. So if you decide not to take on an extra 500 kg of fuel for grandma you WILL over time burn less fuel than you, regardless of points A,B,C and D.
I do agree with your point that commercial pressures from the beancounters should not de a deciding factor. However as a professional you will have to decide for yourself if that extra fuel you take is the best you can do or just plain laziness/arrogance/insecurity.