The reason I like volumetric measurement, even dippers, is for lot to lot consistency. This is all I care about with my pistol ammo, anyway.
For starters, I never leveled the dippers. I just do a heaping scoop.
While there may be a relatively large variability from one charge to the next, as long as the minimum and maximum charges are acceptable, I can repeat that with the next lot. Next year. Or a decade later. And I will have a high degree of confidence that this lot of ammo is the same as the lot I made last time. As mediocre or awesome as that last lot was, this one will be the same.
If I were to weigh every charge with an accurate scale, the variability might be much, much less. But one lot might be 0.1 grains heavier on average than the last lot. This may very well be the way I make rifle ammo. But I will never trust one lot to be exactly the same as another. Because of human error and drift in scale calibration.
Which is why I like dippers and powder throwers best for my pistol ammo. If I already shot 1000's of the same volumetric charge without a failure/jam, I am highly confident that it will work when I make more with the same process. Not to mention, I want the process to be fast and easy for pistol ammo.
Also years down the road, I can look in my log. And I know with which physical insert I made a batch of ammo. My log and these physical inserts are both integral parts of the system. No matter what scale I am using, maybe I even have a new scale. Maybe I dropped my scale. It doesn't matter. When I want to slightly increase or decrease that charge, I will compare the weight of the old insert with the new insert. So I will have a relative measurement - using the same scale, in the same sitting. I don't need to factor in calibration and the operator bias/error (which I'm the same guy, but years of time change my "eyes" and methodology).
You can say I was lax in my calibration. But a human error can't be completely ruled out of any situation that involves a human. I have already proven to myself that I can weigh the same thing twice and get two different answers. The physical insert, once locked down, is subject only to change through the laws of physics.