What sort of investment are you referring to exactly, that thrives more robustly in a democratic setup?
From my understanding, India’s democracy has created a number of hurdles. Your Bureaucracy is infamous.
I dont believe stable economy really depends on a flourishing in democracy, as there are number of examples where the economy has flourished without a proper democratic system in place. Democracy may be helpful in the long run, but is it essential to gaining investment? Certainly not.
There are many countries with a middle class. Indias only appeal is its relative size. Again has nothing to do with its democracy or its supposed stability. If tommorow Indias democratic system collapsed only to be replaced with a relatively stable dictatorship, investors would still show up, just to cash in on the population.
Its Indians that claim their middle class is some grand accomplishment.
There are many countries that are “stable enough” who still dont get very much investment. Infact, many of these countries have environments that are far more inviting for investors, with less corruption, and are simply easier places to do business, yet they dont get nearly as much investment. Chalk the difference up to Indias huge population and smart marketing.