A religion is not successful in relation to other religions. Only in relation to itself.
e.g. a Jew who followed the dietary laws no matter where he lived would still have relevance to the religion, while one who considered the laws of his religion as unnecessary would soon find the society where he lived as more relevant.
A Buddhist landlord who has serfs has decided his religion is irrelevant to his social milieu.
If all Jews and Buddhists decided the way of life as preached by their religion was irrelevant or anachronistic to their society, the religion would die out or be mutated into something different from what it originally was.