Just how many OEs do you have to do to make Arest work at even a 50% chance on 76+ people ? Atm, I have one more mastery of root at 74 and with the lvl 72 one I can root at about 10% if not lower ...
You can't enchant Arrest during C5. You can in Interlude.
As far as how often it lands? It depends on the class you're going after, his or her armor, and his or her jewelry. I don't really even bother attempting to Arrest some of the people that I know have AQ, Baium, and Mental Shield now. It just does not land.
arrest lands more than dryad root... but that's not saying much because I failed 100% with 100 tries on a 78 EE with boss jewels (prolly mental shield too)
im rock'n about a 1% land rate on stun with properly equipt ppls
i can only assume there are no boss jewles on korean servers or they are so evenly distributed that its not an issue