They must have changed their CMYC to RGB conversion algorithm as well. CMYC colors now look different in Preview compared to when rendered in Acrobat Reader or using Ghostscript
I've had this complain (and bug filled) for a long time. They changed it a few years ago, blacks are completely washed out.
But I haven't yet had the inclination to install Sierra.
But I'd disagree. No Adobe software does this by default. Trying to simulate a reflective medium in a emissive one by decreasing the latitude can be useful at times, but simply showing it like that with no option to turn it off seems crazy to me.
And you are right - this started pre Sierra already (can't remember which version)