You shouldn't even be in Defiance for Demon Wall. You can't tank Demon Wall, he attacks random people with Murder Hole. The only time you really tank anything is the brief seconds the adds are alive for. In fact unless you get extremely unlucky and get Murder Hole'd 4-5 times in a row, Regen + Medica II is sufficient to keep everyone healed until the adds and if you kill the adds fast enough one or two Medicas will get everyone topped back off. WHM cleric stance Stone II is pretty strong and not like it's hard to switch it off should you need an emergency heal.