The expectations that healers parse high is not that prevalent in the wider community - healers DPS to different degrees at different skill levels. Healing is generally seen as difficult because of the responsibility you have.
The impact of a botched rotation or mechanic on a DPS is significantly less punishing than a missed heal. You have to care about all mechanics in the fight and there's alot more to pay attention to as a healer.
These challenges begin to fade the higher up the skill ladder you go, making the following statement true: "Healing is more difficult and more interesting at lower skill levels. Healing is less difficult and less interesting at higher skill levels".
Healing downtime becomes a problem (earlier) at higher skill levels because once your party knows the entire fight and has done it plenty of times, all that variability and unpredictability goes away. What you are left with is this game of "how many DPS GCDs can I get away with?".
Optimization begins to happen when you know the encounter well enough that it's trivial. The fun of optimizing broils (pun intended) down to a single goal: maintaining uptime on the boss.
For melee, this means taking risks with movement, doing the mechanic as late as possible, etc..
For casters, this means not interrupting casts by slidecasting and pre-positioning. BLM has a simple rotation, but is still one of the most fun jobs to play.
For healers, this means transforming as many healing GCDs into DPS GCDs as you can.
Optimization happens in two ways:
- Individual optimization, which is basically "how many DPS GCDs can I get away with?".
- Group optimization, which is "how many DPS GCDs can WE get away with?", to the point of everyone knowing their 42nd GCD and DPS/tanks going out of their way to save the healers 1 GCD.
In both of these cases, healing the encounter is a non-issue.
By removing "Heal GCD -> DPS GCD", you would be removing an important part of what makes DPSing on healer fun at higher skill levels.
By moving heals to OGCDs, you are exacerbating the healing downtime issues.
This is an exaggeration, because you have not suggested completely removing healing GCDs. We would be in the same place with perhaps different OGCD heals and different GCD heals. So I am left wondering what problem you are trying to solve. That is why I say that the interesting interactions you suggested can happen with what we have now.
Why shouldn't dropped healing GCDs be punishing?
I disagree with the second statement. The reason why they can't make content require too much healing is because it is too variable and unpredictable, depending on your party. Player consistency would become more important and because consistency is not a strong point at low skill levels it would make the encounter too difficult.
Encounters would be either too hard at low skill levels or too easy at high skill levels - a product of SE trying to appeal to two groups that have different interests and expectations from the encounters in the game.
By setting that expectation you are exacerbating the downtime problem. OGCD healing is the cause of healing downtime.
No content requires optimization. It happens either consciously (people actively trying to optimize) and subconsciously (people know the encounter well enough that they do things they otherwise wouldn't in their first clear).
I do think healing should be nerfed (especially OGCDs) and it has indirectly through the disproportionate scaling of Health Pools. And while this would increase healing uptime - it would merely inflate it, not fix the problem. I do keep bringing up encounter design because that is the only way of adding unpredictability for higher skill levels, where this healing downtime issue is most prevalent.