You are talking about the Didact's personal opinion right? There is your answer right there, personal opinion. He is basically spoiled.
Either way the humans defeated the flood because they injected like a third of their population with some virus, then left them to die. The flood attacked these people and died out, and to get away the humans took forerunner worlds and destroyed those that were infected by the flood.
From my understanding if it weren't for the flood the humans would be able to battle the forerunner and potentially win. It was the flood that caused the humans to lose in the first place, not the forerunner.