I disagree. IMHO, there is no better person than the founder to market your startup passionately.
I am not saying MBA skills are not valuable. But what is more important is ability to write pithy blogs, write tons of emails to your potential customers, investors and do lot of other routine activities to keep your startup afloat. None of this requires MBA as such in the initial days.
Your passion, reading some of the best blogs out there on specific topics is more than enough provided you take all the advice as just that 'advice' and tweak it to apply as per your situation & needs.