Although there is a high correlation between the academic success of the students in professional studies with their entrance exam scores in the competitive exams,caution should be exercised not to stetch it too far.
Imagine an Einstein , C.V.Raman , Iacoca ,or Bill Gates preparing for IIT/IISc/CAT entrance exam.No doubt ,all these people would have flunked the "artificial" settings created by the entrance exam culture,which definitely distracts atleast few potential Scientists/Managers from "real world" work.
Also remember that millions of man hours are spent by highly qualified faculty of disparate instituitions in management or technology for preparing redundant set of questions dished out in all such , highly "competitive" ,exams.And,again, millions of man hours are spent by students across the country to answer nearly similar questions of differnt competitive exams conducted by each separate instituitions, blissfully unaware of the vital waste of human resources!
Instead it should be a good idea to have one common netwide ,nation level exam for MBA or BTech/Banking etc (IIT or Self financing Colleges) through out the country as a routine test every year.