It's unfortunate that we use the term "stronger" to describe wheels, because that leads one to intuit that thicker and heavier parts would do the job better. What we want are wheels that will support the load without going out of true, for as long as possible. Since thin double-butted spokes stretch more, they not only maintain their tension better, but are kinder to the rim, reducing the chance of cracks. So they are a better choice, especially for rear wheels. Perhaps we should be talking about wheels that are more "durable" or "resilient" rather than "stronger."