Hi,
I´m not sure bout this.
The capacitor and the feedback resistor forms a differentiator circuit. (not a high pass filter with a -3dB corner frequency)
It has low gain with low frequencies and high gain at high frequencies.
This may be used to compensate for the first order low pass filter characteristic of the OPAMP.
The benefit is that the output voltage dynamic is not that big as without the differentiator circuit. During the whole bandwidth of the first order section the output voltage should be constant.
But indeed the circuit is not useful to measure DC gain. Additionally this is feedbacked circuit and not an open loop circuit.
As said: I´m not sure.
Klaus