It doesn't really vindicate Gibbon at all.
Gibbon's thesis was that the Roman bureaucracy and army were effectively hamstrung by the supposed flight of the aristocracy into Christian asceticism - sitting on top of stelae, cloistering in monasteries, becoming bishops and whatnot. This ostensibly meant that the people that were left to run the state were, depending on one's charitableness, either drawn from a smaller pool of capable candidates or simply the dross that was left after everybody with a brain went into "useless" "Christianity". This claim is, nowadays, dismissed partially due to lack of evidence, and partially due to the lack of a discernible decline in skill on the part of Roman administrators and soldiers.
Halsall's allusion to altering male gender roles is different, and relates to a different phenomenon, the so-called flight of the curials. According to older narratives, the class of Roman citizens called curiales were responsible for much of the important administrative work in the early Empire. They knit together the fabric of the state by participating in local government, and they were very conspicuous in funding and dedicating civic buildings. But these dedications are increasingly difficult to find as the Empire wears on, with what seems to be a fairly discontinuous break in the late third and fourth centuries; by the fifth century, only Africa saw many dedications by the curiales, and this probably had as much to do with African society's self-conscious archaizing Roman identity as anything else.
Supposedly, the decline in the number of curial dedications means that that class of Roman citizens either stopped existing, or stopped participating in civic life the way they had. According to this narrative, the Empire ceased to be held together in a relevant way on the most basic, local level, and this contributed to its apparently easy break-up and the pronounced regionalism of its later years.
There are several obvious objections to this claim. For one, the decline in curial dedications may simply mean that there weren't many more things to dedicate. A city can only have so many fora and circuses. For another, the growth of the state bureaucracy over the course of the third and fourth centuries provided alternative avenues for conspicuous civic participation. Take the creation of many walled circuits around the cities of Gaul in the third century, acts which received local sponsors much like the walls of the modern German medievalizing village Rothenburg ob der Tauber. State projects such as these received considerable local support, a sort of positive feedback loop as the Emperors were more likely to invest in local projects in areas that they were hanging out in at that time, and it was more likely for there to be local rich people willing to fund stuff if an Emperor were nearby, because Emperors come with a retinue and hangers-on and bureaucrats and the praesental army and whatnot.
But the largest objection is the one Halsall alluded to, namely, that civic participation was channeled into Christianity. Instead of financing public buildings, curials probably started financing charities and missionary work instead. That sort of thing has little to no archaeological imprint, but plenty of attestation in hagiographical sources and contemporary letters, and moreover, it was probably more helpful to the actual populace of a given city than a massive meeting house or magistracy.
Sorry.
I guess taking up my qualms with you won't serve much purpose.
