It is always good to question assumptions. One you could consider is the assumption that all problems are created equal. This isn’t the case. There are fundamental and practical limits to things.
For this kind of artificial muscle actuator, there are fundamental limits to the way the physics works for this design which prevent it from ever simultaneously having good efficiency in energy and power density, high strain and high frequency operation. There are certainly ways to make artificial muscles work, but hydraulics is not the way.
For rockets and space vehicles, the limit has more to do with technology and material science.
For this kind of artificial muscle actuator, there are fundamental limits to the way the physics works for this design which prevent it from ever simultaneously having good efficiency in energy and power density, high strain and high frequency operation. There are certainly ways to make artificial muscles work, but hydraulics is not the way.
For rockets and space vehicles, the limit has more to do with technology and material science.