If I'm following the conversation correctly, it doesn't break anything, the kernel developers don't understand it. Also, the followup from Alex Deucher of the AMD team is interesting: https://lists.freedesktop.org/archives/dri-devel/2016-Decemb... Basically, he reckons that the atomic modesetting code is a poorly-thought out and maintained disaster that regularly breaks multiple drivers - and having somewhat followed the changelogs, I can entirely believe this. (Dave Airlie responds by blaming AMD for not sufficiently testing the upstream kernel developers' buggy changes to their drivers.)
If anything, that post highlights the lack of quality among the amd driver team, and doesn't have to do much with 'taste'.