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Your impression of different depth of field extent and distribution is probably a result of differences in the characteristics of the image and the lenses, such as the noted differences in edge sharpness, rather than an actual DoF difference. Depth of field is a function of the focal length, aperture, etc., and is independent of differences in lens design, so there shouldn't be any actual difference in the DoF results you see.
Well, there is a difference for sure. The 16-35L II is sharp across the frame (left, right and center), the area in (sharp) focus just doesn't reach as deep as the other lenses do at comparable fl's and apertures. The lenses where tested on a fixed camera/tripod position, so the result should be the same like you have said. But they aren't.