Hinduism is more appropriately defined as a complex of religions and cultures than as “a religion.”
As such, to a very considerable extent each Hindu defines his own religion. While most believe in caste, there is of course the slight problem that someone who converts wouldn’t have a caste, since that is inherited.
Not all Hindus believe in caste or in the need to keep lower caste members down.
Whether an individual Hindu believes in caste seems beside the point. The caste system exists ragardless. Though growing up in the South, I didn’t “believe” in segregation system. It didn’t. however, make the separate water fountains go away that I disapproved of them.