Could the division into varnas and castes cause the decline of Indian civilization? Why?

Yes. An increase in social mobility became one of the conditions for the development of society. With the transition to capitalism, people received de facto equal rights and opportunities. The person’s personality received relative inviolability and there was an opportunity to change the type of activity. But in Indian lands, people were tied to the roles that were prescribed to them from birth, and many segments of the population are still deprived of rights.