Hmm..Guess we should start thanking the Muslim rule of India for laying the foundations for an enlightened and prosperous state..Hang on, let's just examine the fate of some other nations which have had the privilege of being similarly conquered and ruled by Islamists. That would include most of the middle east, half of Africa, Afghanistan, the central asian stans and the land of the pure. Now check the United Nations Human Development Index to see how many of these nations (apart from the oil rich gulf states which were dirt poor before they struck oil) inhabit the bottom half of the table. "The most advanced system of governance" didn`t do them much good, did it?
In contrast, India accounted for 33% of world GDP (bigger than the Roman empire) in 1 AD and had a highly advanced economy, legal system and, despite many social evils such as the ever popular among certain circles 'Sati', a free thinking society which gave birth to religions like Jainism and Buddhism and boasted of centres of learning such as Nalanda and Taxila well before the looters arrived.
Economic history of India - Wikipedia, the free encyclopedia
I know its a hard pill to swallow but Islamist rule contributed very little to modern India (apart from fostering enduring schisms within society) bar a few grand buildings, as most of the 'legal and social' aspects of the era that you cite have been discarded by modern India in favour of more progressive western models of governance.
I challenge you to name one major contribution to Indian society that can be directly attributed to the Moghals or the Ghaznavids or whoever? Much of the mathematical and scientific advances of ancient Islamic cultures were largely based on contemporary Greek and Indian thinking, although the Arabs and Persians at the time were enlightened enough not to dismiss it as 'infidel science', choosing instead to build on and refine it.
Before you start, India was unified in its present form by the British and most parts had been governed as a single entity from time to time by many kings in the past, as far back as Ashoka. Even if British had left India as a bunch of princely states, I believe some form of federal structure would have emerged with time due to overlapping cultural and economic interests (much like the present day EU)