Originally Posted by
Zulkhan
Arthas was a good guy too before he became a royal ass. Well, except the fact that Garrosh was never a proper "good guy" as rather a good-intentioned rotten apple.
Vol'jin never stated that, he was talking of the events already occurred on the Broken Shore. He was rather vague about anything else.
Still, I agree that the current storyline seems to push Sylvanas quite far from "raid boss" material.
Cairne disliked Garrosh's brash and disrespectful behavior. Garrosh never had the necessary humility of someone willing to "learn", in fact he wanted things to go his way most of the times. And despite this, Cairne recognized Garrosh's skills as warrior/commander, as well pointed out to Thrall that exactly because Garrosh had potential but had a lot to learn yet, he couldn't be granted absolute power over the Horde. It was a foolish decision and we all witnessed its consequences. Furthermore, I don't remember Cairne ever desiring to leave Orgrimmar or refusing to be Garrosh's advisor. In fact, Garrosh and Cairne kind of came in decent terms until the Twilight's Hammer screwed things up.
Cairne's opinion of Garrosh was absolutely legitimate given what Cairne witnessed of him during half of the book. However, Cairne's fatal mistake was being struck by a sort of "confirmation bias" the moment he heard of his own people killed by orcs parading themselves as Horde members, screwing the very diplomatic meeting Garrosh, strange case, was vehemently against. Given people's general ignorance about the Twilight's Hammer activities at the time, so many hints, the involvement of Cairne's very people and his bias towards Garrosh, it's no surprise that he got his judgement clouded and made him jump to misplaced conclusions.
This said, while Cairne's challenge would have totally been avoidable (even though, hindsight given, killing Garrosh would have probably been a bless) even more avoidable would have been Garrosh pushing for a "traditional Mak'gora" and so a duel to the death for absolutely no reason, "traditional Mak'gora" of which he had zero clues about moreover, requiring him to be instructed by a tauren about orcish traditions.
Also worth adding: Cairne simply had Hamuul's version of the story to judge, who apparently forgot to mention that to the question "It was Garrosh who sent you?" the orc answered "Who?"; that would have been quite a valuable hint on Garrosh's favor.