i go down the list and do each rou every day just by myself and often a 2nd or 3rd time with friends who need it mostly just to get tomes and materia.
i haven't noticed any significant durability issues and it isn't going down to 60% after a single rou either.

are you sure you didn't just switch to a class/job that already had durability loss on its equipment and forget? or you didn't update your gearset? because i just did an ally rou as a level 89 drk and my gear's at 96%ish.