Unlike most fanboys, I will basically agree with this. Hiruzen himself acknowledges he wasn't really that great of a Hokage. He was a good man with a kind heart, but basically an ineffective leader that failed to stop Orochimaru, allowed his pupil to be killed (Minato) and failed to protect the Uchiha or Hyuuga clans. He also failed to keep Danzo in line and would have likely failed to stop Kurama.
Hiruzen is implied to have ruled over Konoha for at least 20-40 years, showing while he may be an effective diplomat and peace-time leader, he is ill-suited to the harsh realities of warfare and human conflict.