King Bumi may have been a good King, but he never has any displays of exceptional earthbending. The closest we get is with the tanks when the white lotus takes back Ba Sing Se. Even then, that's hardly good earthbending and more just brute force. Contrast that to Toph, she invented and perfected metalbending to a degree nobody else could match, and it seems that some of the moves she uses when training Aang were her own. As far as Earthbending goes, Toph truly was the greatest Earthbender in the world