I guess I'm not seeing the "distortion" to which is being referred. The need on a front standard is the ability to place the lens axis at any desired position, and at any desired 3-dimensional direction. The Arca, and similarly designed cameras, enable this capability.
I directly compared a Sinar Norma standard (base tilt above shift/swing) with a Sinar F (base tilt below shift/swing), and the worst I observe is that the latter rotates the lens a bit. But obviously, this does not cause distortion of the image, since lenses are axially symmetric. (Round.)
As for whether or not tilt is on axis, or at the base, it's always possible to use the focus knob in conjunction with other movements, to achieve the same position/orientation of the lens axis with base tilt that can be achieved with axis tilt.
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