Here's how I see it:
The eternal truth is currently (and has been) beyond human expression. At various times and places, those who have gained some acquaintance with the Truth attempt to convey it to others. The results are cults (in the academic sense) which sometimes expand into sufficient popularity (through a variety of means - which often change the original message greatly) to establish themselves as religions.
By nature, any message, any system, must contain some truth. Even random words - even random letters, by their nature, contain some truth-value; some meaning. Lies are disarranged truths; there is no lie without first having the real which is deformed out of accurate representation.
So, all religions contain some truth, the question is degrees and usefulness. Some religions are much, much, much truer, and much more useful, than others. Usefulness is both objective and subjective - leaning towards subjective, and truth is likewise, leaning towards objective.
Some truths are, by their nature, beyond objective referents, they rely on resonance with the perceiver. Utility is much more highly subjective. What's useful to me may not be useful to you.