It's not the gamma. It's like the brightness got twice higher. It's blinding. I wasn't cautious enough, from now on, I understand how extremely cautious you need to be once you have a setup that is fine for you. I could have made so many experiments and possibly discover the problem.
My theory is that the OEM calibrates the display to a certain maximum brightness to achieve the highest contrast possible. This calibration isn't an icc profile. I don't know where it's located. But for some reason, I think a clean install of windows 10 with formatting the main storage disk "erased" this calibration. My second theory is that it's some drivers/bios compatibility issues that where somewhat triggered by the clean install.
I'm trying various things now, like windows 10 1507, windows 8 and 7, bios updates, old gpu drivers. Will see if by any chance, I can turn back the good setup but I have a strong feeling I won't cause the OEM things are not here anymore.