MBA or not?

Depends upon what you mean by "great businessman". Do you mean someone who will attract many employment opportunities with great business potential? Or do you mean someone who will be more likely to be great in a particular business? To be truly "great" in business requires special knowledge about one's chosen field. That is mostly attained by getting to work in that area. But you might need an MBA to be invited to work in the field that interests you. If you can gain entry to your industry of choice without the MBA, then get to work and don't waste time with extending the formal education.