WHM is fine but needs to get rid of a lot of restraints.

1st is overheal. We heal way too much on non and crit heal.
We could solve this by ripping off scholar, getting rid of stoneskin as a skill and turning it into a trait and making any heal received at <100% hp into a soft stoneskin that caps at 18% of target hp making stoneskin useful again as it doesn't require a extra cast and keeping the balance between all healers as 100% heals will not generate shields and somewhat solving the overheal problem. Either that or triggering a mp regen buff everytime we overheal based on the amount overhealed.

2nd is MP management. WHM has the strongest burst heal, burst single target dps and aoe dps. However we also have the highest mp cost per skills, balanced? Yes and no if we look at the other healers. Our mp management only lets us dps non stop for 6 mins non stop before going absolute oom, that time is shortened everytime we heal as whm heals consume a ridiculous amount of mp and with most fights lasting 10 mins WHM falls short on what it should do best, stance dancing.
The overall concept of WHM makes us stay on cleric while our hots deal with some of the damage being thrown out then once our allies are low enough we throw them our massive heals and rinse and repeat till fight ends. This is all fine and dandy on paper but it's impossible on reality in anything that lasts more than 5 mins that has no jumps inbetween (where the bard/mch can safely use ballad without harming his dps).

3rd is accuracy, though this is already somewhat solved with melds. Hopefully 4.0 has a breather on melding compared to 3.2 specially.

More than this is only QoL stuff such as aoe esuna, cure III sized would be enough. Cleaning up everyone on a 8 man party not only takes forever but burns lots of mp even though esuna has the chance of not consuming mp.
Medica I proc actually having a icon so we can plan it over just like we plan cure II/III procs.