I agree it seems rather an overstatement. There were so many forces, many having nothing to do with royal personalities or relationships, that I don't think Edward VII living a while longer could've prevented WW1. I don't even know how much Wilhelm II 'feared' his uncle--while he was Prince of Wales, Wilhelm often went out of his way to 'tweak' his uncle and cause him public embarassment--even knowing that he'd hear about it from his grandmother.
As for Queen Alexandra, she was great at the personal interaction with the wounded, etc...but, yes, organizational efforts weren't her forte.