Originally Posted by
Sagenod
Let's not forget that 90% of the Quel'dorei and even more of the Lordaeronians were wiped out during the Third War, along with certainly many thousands of soldiers from Thrall's New Horde and the Long Vigil Kaldorei. They destroyed the Drakkari Empire as well as most of the Vrykul as you mentioned up in Northrend.
All told in my personal opinion, though this might be arguable, I'd say the Scourge by itself did more damage to the denizens of Azeroth than the original Legion controlled Orcish Horde and the New Horde. Hell even the Iron Horde didn't kill as many people as the Scourge did the way I see it. This is, however, speculative.
Also, I suppose "damage" needs to be more well-defined. Damage to what, exactly? Loss of life or destruction of property and the environment. In terms of wanton destruction of property and the environment, I'd say sure the Horde has netted more damage than the Scourge, which was relegated to the EK and Northrend for the most part. The Horde, especially under Garrosh, went around the world destroying all sorts of shit!