Trapping of hyd pressure in lines is purely incidental and is never relied upon for anything. I've noticed that on some planes I fly (same type and series) pressure goes down to zero half a minute after engine shutdown and on some it can linger for half an hour. Both are considered normal and don't affect normal operation of hydraulics.
Transport category airplanes rely on beefy rudder structure, to withstand gusts, rather than on external gust locks.