I don't know that it could honestly be claimed to be logically grounded, considering it is an attempt to find empirical proof/justification for an entirely personal bitterness that stems from said god not doing as we think he ought to have. When the reason could be as simple as Kasmir just failed at the invocation and had an exceptionally poor choice of words for expressing said failure. Which is exactly what the casting rolls represent in the RPG.
Let me share a secret about academia with you: "logically" in absolutely no way needs to mean "accurately."
Okay, I do have one more argument in favor of Theologian over Dhar Insight, because I love finding me a hill to die on long after most people have probably already made up their minds. If we take Dhar Insight, our peers in insight will probably be pretty much any skilled wizard (hell, maybe even just any
competent wizard) that uses basically any flavor of dark magic. And in practical experience they will inevitably and
necessarily be our superior, barring the thread going full Omegahugger. Moreover, we will almost certainly have at least some peers of equal or greater insight among the Colleges (among other institutions, really), as there are in fact many talented wizards who spend their whole careers
primarily focused on dealing with Chaos et al. They may not have read the Liber Mortis, but an intelligent-up-through-brilliant mind paired with could certainly be half a century or more of practical experience is a long distance from nothing. Which, incidentally, means that any deficits in Dhar Insight that the Waystone Project might hypothetically suffer from might at least potentially be compensated for via the dark power of
recruitment. The regular kind, not the aforementioned Omegahugger kind. Meaning, IMO if you're considering Dhar Insight you should be thinking more about if there are personal actions you want Dhar Insight for than about whether it will enable the Waystone Project to attempt new things; the whole point of the Waystone Project is that it is
not about Mathilde trying to do it all herself.
Meanwhile, who are our peers in insight and investigation if we take Theologian? Uh... Cython, I guess? Who is approaching it (per WoQM) as the draconic equivalent of solving crossword puzzles for fun, not as a serious topic of research. And outside of the tens-of-millennia-old Emperor Dragon, who else is in contention? Probably none of the Cults, since while they've certainly got the personal experience the very idea of this approach sits orthogonal to their idiom. Among the Colleges? There's certainly those who have an interest from the way that Pan-pan and Horstbro talked about their own Colleges, but by the same token they also made it sound like their primary interest is in proving their pre-existent worldview to be correct. Which is not quite what Theologian seems to be for, I don't think. It's also unlikely that they've got the kind of rare-bordering-on-unique encounters and relationships with the divine that Mathilde has had and presently benefits from. Among the Ulthuani? This would be the rare topic I'd say they might actually be handicapped in researching relative to us. Due to attitude, not to lack of ability - the Ulthuani elves appear to feel that divine magic per se is an aberration of human culture (in the best case - the other non-human contenders for users of divine magic are, uh, not great), and hence beneath their notice except to say "ah yes, that's definitely actually something we already understand."
We could literally break new ground in plumbing the very secrets of the universe itself and unveiling the mysteries of the godhead. How is that not the most overwhelmingly sexy choice?? Yes, this is probably the hyped-up take on this option. But IMO you could subtract a lot of hype and still be holding something not just extremely cool but also much closer to unique than any other option on the list.