The specialist company rejects the defects, arguing that it is normal with dark tones and that this is handcrafted and not machine work.
He is right there. Many existing color pigments from saturated colors can cause a problem when painting. By mentioning "handcrafted work," he probably means the brush/roller/paintbrush that applies the paint in overlapping strokes, and where several layers of paint are on top of each other, there is then a different, more noticeable saturation. I once had the same problem with a red wall (solid color).
It would be interesting to know whether the BU, architect, or whoever decided or ordered that the house should be gray, specifically in saturated gray, informed you about this.
And whether the craftsman company simply executes the work or acts in an advisory capacity. Because for me, it is obvious that you can see it. A professional must have that "click" moment and issue a warning about this combination.
I think it hardly stands out on single-story walls.
I personally fundamentally dislike the style of the house but can understand that here three huge disturbing factors (color, height, and windowless wall) are at least one too many. I myself belong to the outliers and go against the flow, but even this is too much for me.