Blending
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A blend is the product where you actually add value, and it is the step most likely to produce two batches that do not taste the same.
Blending is not stirring
Uniformity in a dry mix is a real engineering problem. Particles of different size, density and shape do not want to stay distributed, and the mixing that puts them together is in tension with the handling that pulls them apart afterwards.
The measure of a good blend is the coefficient of variation across samples drawn from different parts of the batch, which in the literature is the number quoted.
The measured hard case
Published work on binary food powder mixtures makes the difficulty concrete and it is not what people often expect. Sugar and salt reach very good mixture quality, 0.03 coefficient of variation or better, at any mixing time. Paprika and salt mix well. Oregano and salt are markedly worse.
The pattern is that two crystalline materials of similar size and density blend almost regardless of what you do, and a leafy herb with a crystal does not. If your blend contains both dried leaf and salt or sugar, that is the hard case and it deserves the attention.
There is an optimum time and you can pass it
Every mix has an optimum, and longer is not better. Over-mixing puts in more energy than uniformity requires and starts to change the material: it breaks leaf down, generates fines, and in doing so widens the particle size distribution that causes segregation.
So the instruction is not mix thoroughly. It is mix until uniform and then stop, which requires knowing where that point is for your blend and writing it down.
Order and method
Bring the components close in particle size before you mix rather than after; that does more for uniformity than any amount of extra tumbling. Add the smallest quantity component diluted into a portion of the largest first, then combine, so you are never trying to distribute a gram through a kilogram in one step.
Tumble rather than stir where you can. And handle the finished blend as little as possible, because every transfer is an opportunity for it to come apart again.