Can you handle the truth? If you want the truth, I'll give you the truth, but don't call me 50 cent.
1) GMAT can be taken multiple times, if you don't score well, repeat it. PISA test can only be taken once.
2) Admission to elite MBA programs is based on a holistic approach, GMAT is only one of the many criterias. Only 3rd-rate institutions use GMAT as main admission criteria, hence, higher GMAT score.
(One has to be deluded to think that IIM is better than top 100 US MBA program just because it has a higher GMAT, LOL)
3) MBA is NO measure of academic rigour. MBAs don't do academic research work, the entire program is about case study and networking. Many MBA textbooks are the same as the ones undergraduate business program uses.
4) QS world university ranking is a laughing stock among academia, the Times Higher Education had to split from QS to form its own ranking.
This QS Global Business School Report is no different. The ranking is based on survey form, how scientific, LOL!!
Don't mean to burst the Indian bubble. Hope you can handle the truth.