When dealing with deformed mesh and UV unwrapping it, Blender takes the deformation of the mesh into account.
But sometimes, you dont want that.
Sometimes, you want a perfect uniform UV grid with no deformations at all.
Besides the unwrapping methods “Angle Based” and “Conformal” there should be a third option called something like “Uniform” or “Grid” where all quads have the same size and are not distorted in any way, like the picture above.
However, I haven’t got any ideas about the handling with N-gons yet, since the “Grid” or “Uniform” unwrapping method is obviously intended for quads only.
Disclaimer: I know, there is an addon called “UV Squares” that you can download and install manually, but despite the recent updates of the addon, it doesn’t work all the time. Either the addon does absolutely nothing or it outputs a python error. The addon only works sometimes. I haven’t found the exact cause of the problem yet, since the addon also once refused to uniformize the UV map of a simple cylinder or a cube with nothing but squares. No triangles, no N-gons, just squares.