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Just expectable to get little gain at switching frequency. As mfntioned early in this thread, there's no useful modulator transfer function above 0.5 fsw. Problem of simplified measurement method is response to components not related to excitation signal.

Yes, as mentioned in post #9, commercial loop gain analyzers are using this method.

Pro and cons of loop gain measurement versus step response have been already addressed. Most practioneers are happy with step response method for stability check and feedback loop tuning and rarely measure loop gain in frequency domain. Nevertheless loop gain measurement is a valid method, opions about unique advantages are obviously different.

Feedback loop can be stable at small signal and still expose large signal instability, in so far I'd rate step response or similar large signal methods as necessary for stability assessment.