Unfortunately, I'm not entirely sure who has a disingenuometer or a factometer, or for that matter, a soulometer to tell whether people really believe whatever or what just say they do. If the theologian believes (whether that's actual belief, or something they think they're meant to belief so they embody it), then it's not disingenuous. If the theologian doesn't believe, and is saying they don't believe, but want to understand why people who do believe what they believe, then it's not disingenuous.
You could equally apply your argument of "passing of conjecture and assumption as fact" as a criticism of philosophy more generally (theology is generally considered a sub discipline of philosophy). After all, Plato's ontology is predicated on the existence of a transcendent domain of ideals to which we don't have access and from which categories get their identity. Kant's ontology is predicated on the idea of inaccessible noumena causing phenomena we do experience. Descartes ontology is predicated on the idea of the mind and body being separated. Lest you think I'm criticising structuralism in general: Whitehead's ontology is predicated on the idea of process underlying everything; Deleuze rejects dualism and hierarchy and asserts identity is a function of progressive differentiation. None of those are provable, they're certainly not facts. They're 'just' conjecture and assumption. And yet those ideas have been incredibly invaluable in helping establish scientific approaches (reductionism is a function of Platonic essentialism; modern psychology often presupposed Cartesian dualism), and opening up new approaches to understanding the world (complexity science is based on Whitehead; Deleuze has enabled some powerful ideas in education, business and other domains).
If you can only study facts, then Newtonian physics should never be taught or studied because it was shown to be unfactual (at certain scales).
And of course, who decides it's a "fact"? What if it's accepted as a fact today, but rejected tomorrow when new ideas and evidence come in? Does that mean yesterday that what we were doing was invalid?
