I think British just re-defined the preexisting system. casteism exist from the day we made our society. In Hindu society it exist from the very beginning, from the era of Ram and Lakshman, even prior to that. basically the goal of this system was to unify society based upon spiritual values and the pursuit of Dharma and Self-realization. but selfish man changed it's values. The system that was based on WORK basis, had changed into BIRTH basis. The one, born in a 'Kshatriya' family will be called 'Kshatriya' doesn't matter what he does.
because of this our lower casts have been oppressed for thousands of year. they have been put off-stream for thousand of years. their rights had been murdered for years.
so after independence, the system like reservation have been implemented to promote these casts. So that they can overcome the loss, can be included in the main stream and become the active part of our society.
ofcourse this system is a clear partiality with "Sawarns" but this has to be done for the sake of the justice, for the equality in society. There can be other ways to give support to these SC/ST/OBC categories, but again those options can not be implemented that, effectively (and without any kind of involvement of others), like the present system does.
Like "School Examination is not the best way to judge a person's capability, But it is the best suitable option to judge one's capability. Because it is the best available option..." Just like that "Reservation is not the most proper solution to this problem But certainly it is the most appropriate available option so far..."