There's no necessity here since we can define our terms as we like. We can just stipulate that "religion" includes institutions that take themselves to be based on historical reports rather than on myths.

My point is about the nature of a spiritually healthy religion. I might even think of it in Spenglerian terms: religions begin as creative cults, inspired by the founder's wisdom. Stories are told to honour the founder or the culture or some way of life. Eventually, the religion's politicized, and the myths calcify, becoming dogmas. The problem, then, is that Christianity happened to calcify early on due to the influence of Rome in the fourth century. Hindus have a healthier perspective on the mythical nature of their theological contents.

But sure, my pragmatic, neo-Kantian epistemology implies that beliefs are on a continuum, there being no purely objective truth. Even concepts taken to be literal often have metaphorical or anthropocentric connotations or underpinnings. The question is how self-aware and humble we are about these limits of our cognitive tools.