Hanzo has a huge impact and is a big part of the problem, but it is Brigitte that gives him that impact.
The OP in this thread was right, that she doesnt even have to be played to make every automatic weapon and shotgun user in the game become a potential waste of time, and can have their power reduced by 25-45% instantly with a single swap (Widow for Brig).
Because the big hitters are hardly affected at all by armor, they become favored (note the instant rise in popularity of old hanzo on OWL when Brig was introduced).
What you have also done was clear the field of Hanzo counters, and his changes made classic counters into characters HE counters (Winston) or who has become a mostly even fight (Dva). The new freedom to operate, along with the much easier aiming, a arrow speed, and Storm Strike, and you have a horrible meta lock, but it is a cooperative effort, brought on by both Brig and Hanzo.