I tried to simulate the effect of common-mode interference on unbalanced sources for three different inputs: single-ended, differential-ended and isolated. Below I inject a 1V common-mode voltage to three identical unbalanced sources(1k Ohm source impedance for positive lead and 0.1 Ohm for negative lead) with identical cables but coupled to three different receiver types:
And here is the AC analysis for the common mode voltage between 1 Hz to 100 kHz:
The above plots show that the single-ended inputs do not reject the common-mode related noise as expected.
But if we compare the differential input receiver's output(the green plot) and the isolated receiver's output(the blue plot), for example at 50Hz the isolated output is 130dB better than the differential-ended one.
Does that make sense? Can we say based on these plots that isolation actually acts as a differential input? Does that mean an isolation amplifier can be more immune to common-mode related noise than a differential amplifier?