Hogan said that he outworked his competitors. He loved to practice. If they practiced two hours a day - no problem. He could beat them by practicing 8 hours a day. From what I've read he worked through the bag every time he practiced - and if he didn't hit the 9 iron as he wanted to, he sticked to it until he did.
I do believe in smart practice, but I am not ruling out that quantity works as well.