I’d say both vol’jin and doomhammer are worse. Vol’jin for doing nothing and doomhammer for throwing away victory to chase some warlocks.
Black hand founded the horde.
Thrall rebuilt it after doom hammers blunder.
Garrosh made it into a actual threat and stopped the alliance from wiping the floor with them in cata.
Sylvanas atleast got it new allies and kept up its tech in the azerite arms race.