As you've stated, this event occurs within the Gothic Wars, an attempt of reconquer by the Eastern empire. It goes a bit beyond the only migration process itself we were discussing here, although it is a consequence of it. Quite sadly, the large amount of deaths actually occured with the attempt of reconquer, Justinian plague etc

It is obvious that nothing is white or black. Yes, violent episodes occured without a doubt throughout the territory, the barbarians themselves were not a unique people, they all had different ways of bringing changes into the places they arrived. The Wisigoths for example did not have the same relationship towards religion than let's say the Vandals. For very much detail, each tribe and place should be studied separately.

Changes were not unseenable, true. They were even needed. Otherwise, the Empire would not have "fallen". But as I have emphasized, this is why the old roman families and clergy was, and has been, very important in the process. Small populations of the countryside were more in contact with their local bishop than the king.