In both cases the companies did better when the founding CEO returned.
I would like to suggest what happened. In both cases the founding CEO had built the company with a clear personal vision. That vision was never successfully transmitted to the successors. Possibly because the vision could not be explicated or possibly because the vision that was explicated was incorrect or off base.
In both cases when the CEO returned they were able to re-establish and clearly elucidate the vision of the company. This allowed them to make the appropriate changes.
In Jobs case, he was able to understand that the final product had to reach his standards of taste perfection. Not simply to master the technology. The early Apple company created the Newton that was a hand held computer (clunky and ugly). The revived Apple created the iPod which was elegant and much more useful than the earlier Newton and when the iPhone came along, it met the demands that Jobs had imagined earlier.
The same is true for Starbucks. Starbucks originally saw its market as the Lefty-New York Times-jazz elite. By the time that McDonald's entered the market a new direction was required. That is where Schultz's return was necessary.
Schultz moved the company toward a much larger but still elite basis. He added Wall Street Journal readers and became friendly to modern workers using their computers at coffee. Most recently he is planning to add high quality pastries.