I largely agree with this, WHM is the quintessential FF healer, so of course its going to appeal to a wider audience of players and having a lower point of entry makes sense.
However, this doesnt mean it cant have a higher ceiling or other healers shouldnt be more mechanically complex. All jobs should have different playstyles and varying difficulty levels.
I dont think healing is easy or boring, this depends on your skills, your familiarity with the content and the skill of the overall group.
While Ive not participated in really high end content yet, Ive played a wide variety of content with multiple jobs to a higher level and I'd say healing can be both one of the hardest and easiest roles to play. I think this might be part of the healer problem, because you dont want to push average or casual players out of the role. But is also why its so important to give roles higher ceilings and more advanced job options.
An idea for WHM specifically:
Split out basic DPS spells. Maybe split Stone/Glare and Aero/Dia out so they are unique DPS spells with single and AOE versions across 3 levels. Obviously adjust Aero and Dias added effects to make them unique. I'd also like to see a few party buffs.
Adjust afflatus so the blood lilly is available as soon as the gauge is unlocked, each afflatus growing the blood lilly by one point as it does. But, have 3 dps skills that consume 1, 2 or 3 levels of the blood lilly.
I'd then tie this together with a magic balance gauge similar to BLM, using DPS swings the gauge to DPS mode, increasing damage potency but reducing healing, while using healing swings it to Healer mode which does the opposite. Basically a light version that contrasts BLM.
When in full tier 3 DPS mode, the spells are comparable to a DPS but healing is reduced a lot, and the top tier spells capable to drawing enimity. So switching into DPS mode comes with risk if you need heavy healing or drawing aggro.
More average players get their safe healing job, but you have a slightly higher tactical ceiling and DPS options for more skilled players.