As a modern recap, Kent Nelson did have control over the powers of Nabu and as time and time went on, the Lord of Order became more and more controlling. Also, Kent Nelson as a vessel was trained to be a host by Nabu so no idiot could just pick up the helmet and have all these powers available. The other aspect addressed by Marty Pasko was the change that Dr Fate was a union between man, woman and a Lord of Order to maximise the transformation, however Nabu kept this information to himself. It was also raised again in the short lived Dr Fate ongoing way back in the day. In All-Star Squadron, Kent knew that Nabu was becoming more controlling and in desperation to find the Kulak controlled Spectre, he had to don the helmet again. So when he was defeated by the Spectre, Kulak thought he could wield his power and Fates... nope... it's not a Green Lantern ring which was also discovered by Glorious Godfrey.