Ok, I reshot the comparison the center comparison (focus is on the branch in the left bottom of the 100% crop):
Left is Sigma landscape orientation, middle is Vitrox landspace orientation, right is Sigma landscape orientation upsidedown (to check if ther's any tilt/decentering impact on bokeh in the center portion of the image) - M DaylightWB ISO100 1/5000s f/1.2.
I've removed previous comparisons, as this one is I hope less ambigous.
I won't comment on what I see so that everyone can make up their own mind .
I think Bastian and Goro were right that my copy of the Sigma might affect the results. Also, next time (if it ever happens) I'll try with a tripod (though I need to fix my head first as it developed sagging with longer and heavier lenses such as Sigma ) to get the framing to match closer.
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) to get the framing to match closer.