I agree with you. Garrosh is physically powerful, but like his father, he is reckless and relies on his strength and bloodlust to overwhelm his enemies - which is why he had problems against Cairne in their duel (Let's be honest, had Magatha not interfered, Garrosh would be already dead and Cairne would be Warchief).
His recklessness already makes him less dangerous than he should be (doesn't even give him a crit buff), but as you said, experienced warriors or even more skilled, lesser experienced ones, would be able to draw him into showing an opening simply by taunting. Cairne did this as well.
Garrosh is strong, stronger than most orcs (I'd say as strong or stronger physically than most Tauren even), but his battle tactics are far too simplistic to overwhelm a warrior of more skill/experience like Cairne/Saurfang/Varian.
And for any Garrosh-lovers saying "Cairne lost because Garrosh is a better warrior," re-read their battle. Cairne is clearly the better fighter, and would've won until Garrosh made a desperate slash, grazing Cairne with the poison and hitting the weak point of the runespear (simple physics - hit the weak point of a long item like a runespear, like the middle, and it'll break), effectively winning a rigged duel. As I said earlier, had Magatha not interfered, Garrosh would be long dead, Cairne would be alive and Warchief and the runespear would not have broken.