If you don’t have hegemony you just need isolation. Bans on premarital sex still work for the Amish and largely for LDS AFAIK. If the group is large enough the isolation isn’t socially harmful. Humans aren’t made to each personally interact with thousands of people anyway, from an evolutionary perspective.
I think religion just needs an update. We have found out a lot about the world since the legacy ones were authored, and actually much of that discovery occurred on a foundation of those legacy religions. We have just outgrown those particular religions. We need a new one.