Kaiser Wilhelm II doesn't seem to have gotten a good reputation among historians. He clearly made a lot of mistakes, but he was also clearly not the only person who made mistakes. Not to mention, there were a lot of other circumstances in Europe that made war more likely.
So the question is: how much was the decision-making of Wilhelm II responsible for the outbreak of WWI? And how responsible was he for Germany's defeat? And how much was out of his control?
The origins of the war are complex, and I don't think many historians would place the blame for the outbreak on Wilhelm. War in 1914 was a culmination of Great Power politics that came to a head after a series of escalating international crises. Wilhelm and his saber-rattling surely didn't help ease tensions, but he wasn't really responsible for the outbreak of the war. Austria's problems in the Balkans, France's desire for revenge from 1871, etc. were all beyond Wilhelm's control.
Once the war started, Wilhelm really lost control of managing the conflict. After he sacked Moltke in 1914, Falkenhayn ran the war the way he wanted to. Once Hindenburg and Ludendorf were in charge, Wilhelm was completely marginalized to the point that German historians refer to the situation as a military dictatorship.