Those brightness flickerings, stutterings and freesync not working still hasn't been solved sadly. Not that they are the only problems, I reported much more bugs over the time since october and no one has been patched.
AMD is interested... but it seems most of the problems are caused by monitors.
Ask Nvidia when they (recently) implemented freesync... they had all sort of problems because of the monitors...
Sorry I was very - very angry I hop is from me power supply is a 750 W I will buy a minim 850 W power supply sun