Definition's like Russell's are religion by assumption, rather than observation. Religions have no requirement to be developed from axioms, or core tenets. Perhaps most crucially, there aren't means to reform and update them universally accepted by their adherents. Comparison of Islam's schools of jurisprudence, rabbinic scholarship, and Christian councils and sect governance, is crucial to understanding how these religions got where they are. Especially interesting, as they are all part of one religious culture.
I go with the argument presented here https://aeon.co/ideas/whence-comes-nihilism-the-uncanniest-of-all-guests that religion performs primarily a different function than presented in these definitions by assumption. That is, a kind of metis, a crafty way, of trying to live meaningful lives together. But, a previous eras metis becomes 'illegible' as modes of life and challenges change. Which is where reform and development mechanisms come in.
I am a flag waving agnostic. That is, not a Russellian agnostic-atheist, a stance of being scientifically agnostic but culturally anti-religion. I see the value of agnosticism as around, not dismissing out of hand all of the 'moth eaten musical brocade' of religion. We have come culturally to see ourselves as purely individuals, with no inheritances, and no real stake in the future beyond our own desires and needs. This is unravelling things like secularism as the cure bitter identity politics, and the ecology and biodiversity of the world that will need sacrifices on our part to save.
Religions have helped us live together, and assert lived values which have benefited us all. And then, helped transmit those values, between generations, eras, even epochs. Philosophy builds a corpus of texts which are there for those interested. It doesn't demand transmission as duty, or even any more to be culturally refined or a good citizen. As postmodern antifoundationalism leaves us fragmenting into ever smaller and more selfish cultural units, we are losing the skills to assert and transmit piditive values and ways to be.
So I am saying there is a religion-shaped hole in our society. There are passionate advocates of filling that gap with science, but they actually get very polarised and bitter even with each other, as they try to take science beyond it's domain. I think we need something more like the aesthetics-cultural embodiments found in Buddhist-infused Japanese tea ceremonies, where architecture, poetry, pottery, socialising, and mode of living, are brought together. We need to advocate not just a body of ideas, but of literature and poetry and architecture, capable of reform and transmission, so that our community values can develop rather than slide into illegibility and fragmentation.