I've always said that the reason that the elements did not WOW TBC Gold respond to him following that incident was not because "he cheated," like so many people like to claim, But because he abused them in his anger. He's still trying to make sense of the reality to this day.
Thrall was portrayed in the battle as serene and sad. He wanted Garrosh to comprehend the qualities a true leader needs to offer, and not be just an apathetic warmonger. Garrosh found it hard to believe that Thrall was failing to understand this and was deteriorating in his mind. He decided to put an end to Garrosh for the good of the Horde.
Also, he failed himself, Garrosh, Grom and himself. He was not able call to the elements, as they sensed his lack motivation and internal conflict.
Garrosh's exposure during fogs of pandaria to the gods of the evil sha that drove garrosh insane and gave him his hulking, dire troll-like physique. Before that, during the Icecrown raid, you can clearly see the garrosh's diminutive stature and the fact that thrall's stature was bigger than garrosh. Also he kind of joined the iron hoard and grew stronger thanks to those orcs.
I'm sure he worked intensely with his "real iron gangsta bros" as he grew larger and stronger.
It is also my opinion that Thrall was not able to speak throughout the fight, because internalized he felt the fault was his own. He was the same up until the time he had a discussion in Korthia with his mom.
He knew that garrosh had to be killed but only as a last resort. It is possible to have cut off his head, cut him with an axe, punching him in the face with the dooms hammer or cut off his head with a blade. However, it might have been too human. He chose to use the electric chair option which let him be killed by one bolt of lightning. It was quite painless to die, I believe. In a split second, lightning strikes and he is unable to maintain his senses and dies instantly from the jolt.
What I'm trying tell you is that the warlord in thrall couldn't take him down. Garrosh's death would have been an even more painful and violent death. Honor is the right of the warrior. The Shaman is the wild one. The elements are more wild and wilder. Push and push them and you'll end up being destroyed by their power almost immediately.
Also, it is possible that thrall has lost his warrior abilities due to not practicing enough. He is mainly using his shaman capabilities in the aftermath of the war in archimonde. Perhaps thrall isn't as cheap WOW Classic TBC Gold skilled as a warrior since the time of archimonde. He's become more warrior-like, and might be able to kill makgora by an axe "for Azeroth!" Just as Helya.