It means "it's no exaggeration to say that~" so the meaning of each sentence is; it's no exaggeration to say that he's the greatest pianist in the world. it's no exaggeration to say that my future depends on this business. It's no exaggeration to say that the outcome of this game was on the effort of the players

과언 means "exaggeration" ~라고 해도 과언이 아니에요 means "It is not too much to say; It is within bounds to say that; It is no exaggeration to say that" 그는 세계에서 최고의 피아니스트라고 해도 과언이 아니에요. It is not too much to say that he is the best pianist in the world. 저의 운명은 이 사업에 달려 있다고 해도 과언이 아니에요. It is not too much to say that my fate hangs upon this business. 이번 경기는 선수들의 노력이 승패를 나누었다고 해도 과언이 아니에요. It is not too much to say that the outcome of this game is dicided by players' effort.