What is the thesis in "The Short Happy Life of Francis Macomber"?

Hemingway’s “The Short Happy Life of Francis Macomber” is intentionally vague and interpretations will vary. I do, however, believe a clear case could be made for the following: Francis Macomber, despite having been killed, ends up the happiest out of all of the characters, because he experienced a personal transformation that Wilson and Mrs. Macomber likely never will.

Macomber felt a wild unreasonable happiness that he had never known before. "By God, that was a chase," he said. "I’ve never felt any such feeling. Wasn’t it marvellous, Margot?"
"I hated it." "Why?" "I hated it," she said bitterly. "I loathed it."
"You know I don’t think I’d ever be afraid of anything again," Macomber said to Wilson . . . [His] face was shining. "You know something did happen to me. I feel absolutely different."

Francis got to experience an apparent end to his lifelong chronic fear, a transformation of the self that lasted the rest of his (short, happy) life, hence the title. He changed for the better in ways that Wilson and Margot, it is implied, never will. This is reflected in Margot’s constant cutting remarks to Francis, most notably her cynical response to his happiness: “Isn’t it sort of late?” Nothing is good enough for her given what she has already gone through, and she doesn’t see positive change as valuable if it’s happened after considerable time and effort. In her mind, whatever good that happens should have happened a long time ago. And after she shoots her husband, Wilson treats her with condescension, and she continues to be upset—in other words, her life isn’t going to get better like Francis’s did.
Wilson, for his part, continues to be cruel and controlling. Cruel in the sense that, while he is disappointed that Francis was killed and says as much, he doesn’t express any large amount of grief or distress. His disappointment is more in Margot’s behavior than in Francis’s death. This is reflected in the last line: “‘That’s better,’ Wilson said. ‘Please is much better. Now I’ll stop.’” He seems to be more interested in holding power over her than in making her see the error of her ways. Neither character is any better off for having killed Francis, while Francis, though dead, experienced a complete character transformation.