Comparing differential-ended and isolation amplifier outputs for an "unbalanced" source input
All models are faulty, unless you make them as accurate as possible.


Include stray common mode E-field impedance or capacitance for cables 
transformers have a coupling capacitance and they are mismatched


Baluns, GFCI's and Hybrid Splitters are better than normal transformers due to these balance requirements.

input output impedance matters for both CM and DM to get CMRR  


this is why CM chokes with X,Y caps are used for line filters to achieve CMRR for FCC,IEC immunity and lightning suppression.