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That's the thing I find about Zeiss stuff. There are a great deal of references to "character" or "colors". Things like sharpness, CA, LoCA, vignetting, maximum aperture, and AF speed / accuracy are all measurable, and, according to PZ, the Sigma bests the Zeiss. I like Zeiss' stuff, but I think that there is some confirmation bias that goes into some of the Zeiss mystique.
A couple of things to keep in mind. First tests especially done with imatest software do not capture all that is important about images. Imatest is good at looking at sharpness at fairly close focus range, but even that is limited as it is presented in most tests with only focussing on two or three points across the frame. It gives some information, but it should not be confused with a definitive measure of sharpness. In my view the CA tests are even more limited because CA shows in different ways with different lighting conditions and they only test with one type of lighting situation, and it only tests for CA in the focus plane. PZ does take a shot of a ruler to look at longitudinal CA (CA not in the focus plane) for some lenses, but again this is only a very rudimentary tests and only captures this type of CA in one pretty limited situation. So, yes the Sigma 35 f/1.4 art lens does test better at PZ and whenever imatest software is used, but this should not be confused with comprehensive evidence the the Sigma is better.
Second, one area in which the Zeiss ZE 35 f/1.4 excels is in its bokeh. Some test sites set up a scene and provide a little evidence about bokeh, but bokeh shows itself in many distances and many backgrounds so this is a very limited test. I can say, however, after using the ZE 35 f/1.4 that it has lovely bokeh in a wide range of distances and backgrounds. It is in my view the primary strength of the lens and one area, IMO, that is is much better than the Sigma.
So, I think the Sigma 35 f/1.4 Art is a sharper lens at wider apertures (but not stopped down) and has less CA in some situations, but I think the Zeiss ZE 35 f/1.4 has much nicer bokeh. Which lens is better in my view depends on how one wants to use it. Stopped down they would both be excellent for landscapes. Used at or near wide open I think it depends whether the bokeh is going to impact the photo more or the in focus region. Both are great lenses, however.
my 2 cents
Edit: and by the way PZ doesn't even test the ZE 35 f/1.4 or the ZF either so there is no direct comparison at that site. Lenstip does test them both, however.