I can't come to a definitive conclusion because I see conflicting evidence on gameplay videos due to different scenarios. I don't own Ryzen but I've seen it holding back a GTX 1080 in certain games. But even then it performs just fine unless you're obsessive compulsive when it comes to maxing out performance.
To answer the original question, a GTX 1080 is only overkill at 1080p if your monitor is 60Hz.