if u take that litterally .; then AST with foresight should be the shielder. Usually wards/shields/prevention magic is linked to foresight.

SCH should then buff allies more and at same time .. how do u recreate the strategic maneuvering ? give them lots of tools for the different situations --> which they have. jack of all trades ? now .. a jack of all trades can easily be OP or UP.

WHM is still powerful healer. maybe a way to make them unique it to give a group invuln with ofc long recast. buuuut ... seeing how game is designed, would u really want that on a healer ?