It sounds like the basis of your question is: what's better experience or MBA
Honestly I don't think they're necessarily interchangeable -- they build on each other -- that's why most b-school programs require full-time experience.
Do I think that everyone who wants to be successful in business needs an MBA? Of course not. But it's a great way to formally learn the fundamentals of business, build a solid network, test your ideas and make a transition in your career. I wouldn't give my experience up for the world -- and I think most of my classmates would agree with me.
Overall I view going to b-school like learning to become an artist. While the greatest artists are great because they deviated from the standard protocols, they first had to learn the standard protocols in order to know when / how to deviate.
A lot of marketing managers who learn how to market based on their experiences are myopic in their thinking, because they've only seen one style. Whereas a b-school, the point is study a ton of different models and gain exposure to multiple industries / approaches, which then can be applied cross-function and cross-industry.