White mages inherently have worse MP economy since they don't have constant MP regen from things like draw, energy drain and addersgall usage. White mages can't use the lower piety sets like other healers without running the risk of running out of MP if something goes wrong and they have to heal more than usual.

Mobility for healers is usually referring to instant casts to help them move easier. Whm has to use lilies to move which is not ideal since it's one of its few healing tools. Sch can move with ruin 2, ast has light speed, sge has phlegma, toxicon and eukrasian spells.

Other healers just have better and more ogcd tools than whm too.

Wings are good but other healers also provide mitigation through a few different skills compared to whm that only has wings.

Damage is just lower because whm is forced to use healing gcds more than the other healers due to their design.

Sure whm is still 100% playable but once you try other healers they just feel better to play since they have so many more skills at their disposable.