Could dual cast or some other mechanic like it work for WHM? Like, WHM gets dual cast, and it also gets chunky stone, and aero spells to use it on -- they could even give them cleave to be hotbar space efficient. Or casting Glare grants stacks of Tranquil Hearts or something which reduce the cast/recast time of specified spells like the previously mentioned aero, and stone spells as well as healing spells. I've mentioned this in an other 'boring healer DPS' thread, but I feel like if there were any jobs that WHM could take inspiration from to create a potential DPS rotation they would be either RDM or BLM.