I have worked for several such companies, and at one time I was Information Coordinator for the American Marketing Association, so I've been exposed to a lot of marketing 'genius'. One thing I noticed time and time again in all these places is the prevalence of 'internal marketing'. When stripped of trendy buzzwords and platitudes about 'empowerment', internal marketing is a De facto ideology which stipulates that marketing is the primary driving force in every organization. It places product quality, customer value, and strategy in a distant secondary position.
The problem with marketing companies is that their myopic focus produces reactionary organizations - more ad hoc institutions than enterprises. 'Marketing companies' are sometimes profitable, but rarely maintain a commanding market position for long if they get there in the first place.
Contrast these with the real product companies of our time: Apple, Google, Craigslist, Facebook, Toyota. The real profit and value are being created by companies who focus on actual products. Some of these companies have little marketing apparatus at all, at least in the sense you're talking about.
This reminds me of a silly aphorism: You rob a bank because that's where the money is. Providing seed funding to 'marketing geniuses' is like robbing twenty hot dog stands and hoping that one of them forgot to deposit their earnings that week. It's only a good plan if you can't figure out how to rob the bank.