You make a good point, but here's how I understand it - and I'll cop that may be wrong Diocletian's reforms did a lot to recentralize the empire, but by the th

You make a good point, but here's how I understand it - and I'll cop that may be wrong Diocletian's reforms did a lot to recentralize the empire, but by the the late 300s during this influx, the nation had been wracked by the wars of the tetrarchy, and a cavalcade of small civil wars instigated by would-be usurpers. The iirc military relied more heavilly on conscription, and the better part of it was deployed in service of the emperor's protection, leaving border territories defended by fewer units more dependent on local governing authorities to provide supplemental irregular forces. The instability at the upper tiers of Roman government from successive administrations executing purges in various states of paranoia, the vacillations between administrations favoring/disfavouring Christians in different quarter of the empire, and the empire's financial troubles had also done a lot to degrade the Roman bureaucracies institutional knowledge, and capacity to plan/execute policy. As a result, the roman empire was institutionally incapable of managing an uncontrolled mass migration of the scale that was instigated by hunnic expansion in eastern Europe. This wasn't just a matter of being incapable or too miserly to integrate germanic soldiers into the military, it was a matter of integrating entire nations into Roman society at a scale which Rome had never before experienced in a context far more complicated than an occupation of foreign lands. Irrespective of their pay, Germanic soldiers weren't effectively granted a place in Roman society because Rome had no capacity to give one to them or their families, and at the same time did nothing to prevent them from staying connected to their tribes or their leaders.