Machinburd:
That basis is that normal hydraulic pressure is available. If hydraulic pressure surges up and down as various elements of the flight control system are actuated, the predictability of all the engineer’s control studies goes down the toilet. The controls will move in unpredictable non-linear ways and induce additional time lags. That is the thesis of the second pathway to loss of control
Seems to me that an "inner loop" driving the control cylinder rate and/or position to the pilot/autopilot requested values would have to exist.
This would remove the influence of instantenous hydraulic preasure variations. ("surges up or down"
This is similar to using feedback around an op-amp to precisely set gain even though the raw gain of the amp may vary 10:1 or more.
If the available raw "gain" (hydraulic pressure) is too low then the inner loop will fail but that would represent either a fundamental design flaw/or hydraulic system failure.
I am not familiar with real world details (work in electronics not hydraulics) so welcome insight from those who do know.