These are thoughts that actually came up after I wrote about theology and philosophy earlier this month, although they could be applied to most any ancillary discipline with which theology often finds itself concerned. A basic difficulty for doing theology seems to be that it requires a good deal of legwork in other disciplines just to get its own work off the ground, which inevitably means that theologians trying to take adequate account of philosophical, historical, text-critical, or other contributions to human knowledge relevant for the explication of the doctrine of the faith will come across as dilettantes who know just enough of another discipline to hurt themselves. For the moment I'd like to think about this difficulty as it relates to historical work done by the constructive theologian.
One of the things that I find challenging about theological work is that for the most part, we are never simply offering a theoretical account of some aspect of the doctrine of the faith. Most theologians, that is, wouldn't write a treatise meant simply to offer a coherent explanation of "revelation". Rather, any coherent explanation of revelation coming from a theologian would likely consider an historical tradition of thought leading up to the present constructive presentation. In some cases this reliance upon previous work on doctrinal concepts is more implicit than not, but theology on the whole remains a strongly diachronic conversation- and more so than other disciplines (although any discipline will engage with the previous literature in some way) because of theology's status as a discipline born out of and informing a doctrinal community. This history of theology isn't simply raw material for analysis; it is something that also holds theology to account through certain orthodoxies or pious expectations for theology's development of the self-understanding of the faith. (Incidentally, this is why I think that the idea of theology as a re-conceptualization of the faith for the present day is a bit unhelpful. It leans too much upon a metaphor of succeeding pictures of the faith, and does not adequately convey the extent to which tradition is not a mere correspondence of ideas with where-we-stand-now, but rather a recognition that the faith lives now, and we can engage with it.)
But the work of the theologian as constantly accounting for and being held to account by an extra-theological faith tradition makes the intellectual work much less straightforward than someone simply engaged in history. A theologian for whom the proliferation of 20th century Augustinianisms is relevant (however much some of these 20th century versions are only really pseudo-augustinian) is never going to be able to match up with an Augustine scholar's ability to offer an historical account of Augustine's thought within its original context. Too many competing receptions of Augustine remain important for the theologian to incorporate that are simply irrelevant for the historian of Augustine, who only really needs to see these receptions as later history that got Augustine himself either more or less wrong.
To make matters even more gloomy for the theologian, you rarely see a constructive theologian that remains simply Augustinian to the extent that you might see an historian whose published work doesn't venture outside of the third to fifth centuries centuries at all (with half of the work being about Augustine himself). It's not just the whole of the Augustinian tradition that keeps theologians from acquiring an adequate historical account of Augustine, then, but also a sustained attention to Pauline thought, or a denominational context of Methodism, or an interest in theological bioethics... and would a constructive theologian with all four of these already-incredibly-broad areas of study represented in their CV look at all out of the ordinary or generalist as far as theologians go? Hardly. One could easily add to such distractions from a comprehensive historical engagement.
I don't know if there's much to do about this difficulty, and I don't see it as a bad thing. I think that theologians should be focused on a wide variety of topics if they're going to offer any sort of compelling systematic account of the faith in their career. Theologians whose expertise is limited in scale to the equivalent of "the Petrine epistles", or "the problem of evil", or "late antiquity" don't really possess the tools to offer a constructive account of the doctrine of the faith, and theologians who do intend to offer a constructive account of the doctrine of the faith don't have the resources to speak to 1 Peter in the way that a biblical scholar might who has spent the last five peer-reviewed articles and a book writing about it.
I'm something of a generalist, so I take this to be an exciting challenge for the work of theology and not anything limiting. But discouragement does continue to pop up for me every time I present an occasional sort of paper on a topic that others have devoted entire careers to unpacking. Anxiety in such instances is, I think, best channeled towards better theological work and not towards an inferiority complex with regard to neighboring disciplines.