Sea Breeze, I have not read of any experts who discussed the fact that in the expression "God Jesus Christ", "Jesus" is in the genitive case, which has to mean "God of Jesus". This is Greek101, unless you can suggest an alternative translation which takes the genitive case into account there is nothing to discuss.
As for the inscription which credits Gaianus, also known as Porphyrius, a Roman centurion, for funding the mosaic as an act of generosity, this is hardly surprising as there was a Roman camp right next to the village. More than likely, in my opinion, his family lived in the village and probably attended the prayer hall. In fact, another inscription memorialises four women who may have been related to him. I certainly agree it seems members of the Roman army were allowed to be part of the Christian community (as were members of Caesar's household), but the army served in both an administrative and a military capacity so that may be reflected in the Christian position. A bit like our civil service, if I was to draw any modern comparison with their function at that time and place.