I think if you compare across all MBA programs in the US and all CS programs, and account for debt, you'll find that the average CS program has a better return. This is because even shitty MBAs cost a fortune and don't necessarily teach a lot of useful skills, whereas even a shitty CS degree teaches you to program enough to be employable.

Now if you compare a Harvard or Wharton MBA to say a Stanford or MIT CS degree, then you'll probably find that the MBA outperforms by miles. But I think that's because those programs sell a deep network of rich and powerful people. Harvard MBA go off to run large companies, and Stanford PHDs go run research projects. I'm generalizing, but at the top end they're using very different optimization functions.