OCR is indeed religious studies. There is about a 50% cross-over, both contain arguments about God's nature/existence and debates over ethics/morality.
However, only philosophy contains epistemology - debates about whether we can have knowledge. Philosophy also focuses on the philosophy of mind, the debate over whether the mind is just a physical thing or something more. OCR have one topic out of 32 on this, but in philosophy it's a quarter of the whole A level.
In religious studies, 1/3rd of the A level will be the study of religion. Most schools choose Christianity. This is half about general debates around the main features of the religion, and half about contemporary issues facing the religion (e.g. feminism, multi-faith societies, secularism/secularisation).
Honestly both are good. Both require proper revision strategy, lots to memorize.