Very correct. Caste system is a social system. It has nothing to do with Hindu religion. It is as good as arguing that slavery of Blacks has been an integral part of Christianity.
Slavery of Blacks and oppression of Dalits are strictly social problems, unrelated to religions.
That is why even when Dalits convert to Christianity, caste remains and dalit christians have separate churches or pews. If it was a religious problem, it would have been solved by conversion to another religion. It is not solved because it is a social problem, not a religious one. Even Muslims have castes and a rajput Muslim will never marry with a dalit muslim. It is clearly a social problem.
This argument that caste oppression is equal to Hinduism is a mischief propagated by Christian missionaries for conversions. Some stupid Hindus lacking intellectual depth fall for it and start apologising.
There is an easy solution. Whenever a white man or Christian talks about caste system, you start talking about how Christianity is responsible for slavery of the Blacks.
