Fabio,
I have just checked on my 7A26 and the Low Frequency Compensation (attenuator) adjustments do have about the correct time constant to correct for your 3usec lag in response (I only checked one of the attenuator settings, 0.1V and C114,C115). You could try using the 7A26 LF compensation to flatten the 1 - 3usec region before going back to the mainframe adjustments for the higher frequency components. I am sure you can see why the standardizer plugin is useful - you have HF compensation both in the mainframe and the plugins.
I think the sharp 'knee' you have shown on the YT video is due to trying to correct the low frequency error in the plugin with the HF adjustments in the mainframe. Adjusting the lowest frequency / latest time errors first reduces the interaction between the adjustments.
I hope I am helping rather than adding confusion, best wishes,
Roger
