A diverse country can never succeed in a democratic set up, that too a parliamentary democracy. Its so easy to divide people based on three aspects : caste, religion and region. This produces leaders of communities/regions etc who will essentially become over powerful. Thats exactly what has happened in India.
We have not reached even a quarter of our potential. If india had a strong dictator like Sardar Patel or even Modi ( though i hate his divisive politics), we would have been a developed country