baseless claim but feels right: the most socially beneficial religion would be moralistic therapeutic deism but with 1) a high ritual default and Really High Ritual opt-in lifestyles (ascetic practices designed to produce mystic experiences, options to be a high-status volcel, etc) 2) the option to say “oh yeah that’s all garbage lol” while still participating in all the outward rituals and rules, like how Judaism sometimes allows for that kind of orthopraxy
(when people say “x is a religion” dismissively i’m not sure why that’s a bad thing, the thing that’s wrong with most religions are the premodern survivals in ethics and metaphysics (when those are even present), not ritual, beliefs, etc; so you could probably build up all the above from existing “secular” culture and largely we have many aspects of this in a sort of prodromal form)
If you’re separating metaphysics from beliefs, something has gone very wrong somewhere.