Is Willpower the Only Skill to Develop?

Simone Vay was a big fan of stoicism. She wrote in her early journals that willpower is something that kept her on the moral path she wanted to be on. But you try to improve yourself enough in this life, isn't willpower useful? Is it even the best skill to develop? What if instead of getting super good at forcing yourself to do the things you don't like, you got super good at reimagining the things you get no joy out of to be things that you do get joy out of?"