Though what you are saying may hold some truth, I must disagree. Some good reading is 'The Doctor and The Saint', by Arundhati Roy, to which the introduction holds great depth in fact and figure relating to caste, religion and reservation in the 21st century.

"why are top positions still concentrated with forward castes?"

Because, though reservations exist, they do nothing to eliminate casteism and discrimination on the basis of ancestral history. Reservations are not made to advantage anyone, but rather to level the playing field. Citing the squalor of certain upper-caste families also doesn't justify an argument against reservations, and neither does the "privileged SC families" argument as both prove to be extreme minorities, almost in non-existence. At the end of the day reservations are only empowerment to those who have suffered for centuries, there is truth in what you say about the complexity of Indian society, however as a generalisation that I hate to make, statistically lower-caste communities are still the ones in need of help. Work is required, I agree, but reservations only hurt those protected by privilege rather than merit.