Update:
Just discovered that a MacBook Pro (Retina, 15-inch, Late 2013) using 802.11 ac is also affected on the 5GHz WiFi.
Very similar to the Nexus 6P, ping and low-latency video streaming issues.
Another MacBook Pro (Retina, 15-inch, Early 2013) which only supports 802.11 a/b/g/n is not...