Since long established facts in academia are rarely known on Twitter, here's Richard Gombrich (pic 1) stating how Brahmins and Kshatriyas formed bulk of the Sangha.
Furthermore BG Gokhale (pic 2) cites the Anguttra Nikaya as a record of the Buddha himself listing monks and nuns who should lead the Sangha. The Brahmins and Kshatriyas top that list too!!
There's isn't a single religion that wasn't devoured by caste. From Buddhism to Islam and Christianity, in India caste infests all. If you are looking towards religion to annihilate caste you are anyway doing it wrong!
Even the Sangha was divided along caste lines.