That's the story of Space Seed. Wrath of Khan is primarily concerned with Khan's revenge. I love Wrath of Khan, and definitely the balance of the space opera and the science fiction elements, which comes more from the Genesis device, is handled much better than in JJ Abrams Star Trek. But the sci-fi elements are more like McGuffins and subplots in both films. They aren't the primary concern.
It's also the story of the Wrath of Khan, though Khan's motivation switches from ambition to revenge. Why? Because of the sci-fi concepts of what happened on Ceti Alpha V. (Note also how he compromised Terrel and Chekov.)
And, of course, he still has his ambition, which is why he wants Genesis.
It's not a MacGuffin - Khan being who he is, and WHY he is, is central to the plot.
