Bleeding hydraulic systems (of air) is a common requirement, although some have self-bleeding capabilities built-in if working correctly.
Hydraulic fluid is essentially incompressible but a tiny amount of air can compress easily making a hydraulic cylinder act mushy, like an air spring.
I would hope the owner's manual addresses bleeding requirements if they are needed. In any case, I would look at the stabilizers (without getting under RV) while someone is moving around the RV to see if I can see any movement of the cylinder rod going in and out. It shouldn't move at all if working right.
It's hard for me to imagine that a hydraulic cylinder bolted directly to an RV chassis wouldn't be much stiffer than the RV's suspension and tire's if it's installed and working right.
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