I see people come to pursue an MBA degree solely for the purpose of getting into a better business Ph.D. program, but it's rare to do so mainly because of the costs and time. However, if you can get decent scholarship to some top 50 MBA program, then it is possible to continue your Ph.D. program at the same school. Generally, the business Ph.D. program is much more difficult to get in due to limited number of spots available in college of business.
Do whichever you believe worth doing regardless what others say.