Many Christians actually preserve their cast system practice even after being converted to Christianity. So not sure how exactly it’s is an attack on cast system.
Lot of “lowest cast” members convert under material enticement, and then reconvert back to their original religion. Easy come, easy go.
The caste system is integral to Hinduism, its polygamy. So the analogy of keeping caste is analogous to a person converting to Christianity but keeping his national customs, which might include some rituals relating to the tribal god. As far as material enticement, many A Christian lad or lass goes to college and there gives up his/her faith in order to fit into the secular world he/she finds him/herself. Much of India was converted to Islam in order to avoid the tax. Edmund Burke’s Anglo-Irish father raised him as Protestant so he would not be barred from the public service.