Again with the cherry picking, Thrall is a shaman, he calls upon and then controls the elements. The elements are Thrall's weapons along with his Doomhammer.
Mak'gora
The no armour you're thinking about is nothing but a loin cloth over the genitalia of the person, evidence in the picture below.
Garrosh was still wearing leather, plate, wristbands, fur and goddamn chains in the cinematic.
Hell, Garrosh and Thrall have already dueled in a Mak'gora with Garrosh in full armour and Thrall using his elemental powers, evidence below.
Comic
In-Game
even a video showing Thrall using his powers,
The comics they didn't bless there weapons either, obviously Mak'gora word has taken on more of a meaning then what you are saying.
You really need to let go and just accept that Thrall killed Garrosh fair and square.