Different strokes for different folks I guess. To me the match was nothing short of brilliant.
It's definitely not going to appeal to detractors of the strike and fighting spirit heavy version of Puro, as these two guys are the pinnacle of that in modern wrestling, but it no doubt told a well executed story.
Reading it called "fake" blows my mind. Understand that the story being told makes the match execution different. Ishii and Shibata are in a constant tug of war over being seen as the toughest and stiffest strong style wrestler in the world. At any point that they meet in the ring, even if its a random couple minutes in the middle of a multi-man tag, it becomes a game of one-upsmanship with both men determined to prove they are tougher than the other. Its like the Japanese version of "machismo"(call it "samurai spirit" or something else probably borderline-racist like that), and on a gigantic stage like a title match at Wrestle Kingdom that same familiar game just naturally gets turned up to ten. Which all explains the reasoning for the spot trading exchanges that you classified as adding to the match's "fakeness".
As for the head-butts, I thought most of them were well-timed and laid in pretty stiff, especially the last charging one to the chest that Ishii laid out Shibata with in the final minutes.
Considering the match tells a logical story(and does it excellently BTW), the overall stiffness of the contest seems to me to make it quite possibly the furthest thing from "fake" that you will ever see in pro wrestling.