But seriously, saying he is weaker than Illidan and comparing him to random bosses is sacrilege imho haha. Lei Shen is really strong, maybe stronger than any other mortal warrior (as in Varian, Garrosh, etc).
"Ah... you have learned much... and learned well... an honorable battle.
In the end, I stood by the warchief, because it was my duty, and I am glad that it was you who struck me down.
May your strength... lead the horde... into a new era of prosperity..."