I've worked with or for many managers in my professional careers and some of them had had MBAs and some of them have not. In my experience, I have not noticed that managers with MBAs are not significantly better than managers without them. I've known great managers with MBAs and great managers without them. Leadership can take many forms and I'm just not convinced that an MBA program is the best way to improve those skills.
An MBA gives a person skills in business and also teach the person how to manage people but it does not teach someone leadership. Leadership is learned through social experiences and the out look that the person has on life. You can take classes that may help a person figure some things about leadership but that is really about it.