Is Kenta actually mad or is he just a fucking great worker? I don't know the answer.
At first, he was mad because in Japanese wrestling culture, and really just being a good human being, if you want to use a move then you get permission from them. This isn't always the case as there some moves that are just super universal and have become common that it isn't really needed. For example, Falcon Arrow, Michinoku Driver, Lariat, Blue Thunder Driver/Bomb, and a couple more. But the G2S is different since KENTA created it, and was the only person using it like how Manami Toyota created the Bridging Straight Jacket Electric Chair Suplex, and only two or three people have permission to use and when Bea, Blair Davenport in NXT, began using it Manami wasn't to cool with it.
As for now, I think KENTA is still a bit mad, but he is working the people who want a KENTA v Punk match due to everything I mention and the fact Punk gets the credit for the move and he doesn't. Same for the Anaconda Vice as well, in which Tenzan created. And again, I am one of those people who wnat it to happen, but I also meme it as well so I am taking fair shots at myself.
(I will wait for the for "fuck that shit. it is dumb" response, but Japan is built based upon respect and most of the old wrestlers aren't dicks like when Go Shiozaki began using a Inverted Scoop Brainbuster, Akira Hokuto thought it was cool and said he could use her version, but he was like "nah, I am good, but thank you")