yeah no... as someone who is lucky enough to be good friends with a camera store owner im siding with the my brother works for rimac guy.
i think i might be wrong by +/-20 but i believe that so far i have worked/shot with somewhere around 650 lenses, again, i may be wrong by +/-20 lenses but yeah, as well as with somewhere around 80 different camera bodies, all from Nikon, Canon, Sony, Fuji, Panasonic, Pentax, Olympus, Leica, Hasselblad, Minolta, Contax... You name it... and by far the best quality of an image, like actually drastically visible difference in image quality, i saw from using Voigtlander, Zeiss, Leica and Hasselblad lenses over every other piece of glass i have ever used... ESPECIALLY Zeiss and Voigtlander!
when he says sigma, tamron and others render flat images and with no micro contrast, i believe he refers to the way the lenses render separation, distance and shape of different things of different colors at different distances in the image. they render them flat as if they were layed out on a piece of paper, instead of separately and naturally as you would see them with your eyes or as if for example a Zeiss, a Leica or a Voigtlander lens would render it! that's what he probably means and i agree because the difference is just absolutely huge and its such an improvement over modern lenses that as he says render flat images (which by the way, micro contrast is indeed very, very real and very very noticeable, especially in images shot in sunrise/sunset or studio flash lighting AND even more so when you shoot B&W) and all of that, all of those characteristics are just as he said, thanks to apo glass, aspherical lens design, micro contrast and the way the glass reads light bouncing of differently spaced things and sends it to the cameras sensor.
i've shot on hundreds of lenses and dozens of bodies and you only see such immense quality in the images shot on Voigtlander, Zeiss, Leica or Hasselblad lenses.