You say: "What, if anything, do we have to gain from denying that these modern attempts to create meaning are functionally religious?" Indeed, denying that modern (and other not-at-all modern) philosophical attempts to give life meaning share the same function than religion serves no purpose. But the problem here is a lack of clarity: where religion gives life meaning via faith and belief, philosophy at least attempts to answer this existential question by reasoning and avoiding illusions and false statements. This is a rather useful distinction, isn't it?