Okay on the setup, that might be where a few things get muddled in your delivery. That's semi why I got confused with ED and Aetherflow.
As for Libra you aren't wrong in your "description" of what the sill can do, but it's a bit miscalculated, I guess is how I'd put it. Based on what you said, you'd be trying to bolster your own defenses, which falls under the healer/tank umbrella. But a skill that does that would be something to cast on the party, not the enemy. Additionally, while it does do both, what you made was a merged version of Feint and Addle. Unfortunately, with the new BLU Condensed Libra added, it shows SE is more inclined to have it focus on offense than defense. But I wont say just forget it, I'd just suggest finding another way of implementing the skill.
As for ED and Aetherflow, the current system is best, sorry to say. With your system the stacks might become too commonplace, and management would be almost nonexistent. SMN doesn't need to manage stacks, but SCH does. Plus, there is no skill to burn excess stacks. That's part of the reason SCH was given back ED in the first place. Your system sounds alright in theory. But since both grant stacks, you'll wind up having more than you'll need once the skill is off CD. And to use a stack on an unnecessary heal is just bad. It would be better if one did damage and restored MP, but at that point it's the same as the current system, just different CDs.
As for the SCH theme. Well let's be honest, has expansions come and go, their theme is muddled. But the basis is a tactical healer with a pet. So as far as wanting to make more pet-centric skills, yes that would be welcomed by almost everyone; though I would be careful on the potential fluff. Some things might sound cool, but if you think about some things rationally, you usually can trim a lot off. ET was mostly just a skill that supplemented their lack of raw healing, but I wouldn't say it's entirely "bad" but it could get added usage in other places, maybe make it a 10 second buff instead of a one time deal. That fits both it's current theme and your idea to bolster their heals. And while Dissipation is still the least favorite of the capstone skills; thank god ED made it useful again, I am all for a healing buff that doesn't lock out part of the SCH kit. Neither WHM nor AST lose any of their kit when they get their buff, regardless of SCH getting it 20 levels earlier.
As for the other healers. I understand the idea for all 3 wanting a rework. Though, I am surprised, even WHM? Isn't this like their best version to date, so I hear. Mostly because of the whole heal/dps issue they don't have as much now. Anyways, the main thing is to consider how a skill would interact/compliment the other healers, not necessarily redoing them as well. Basically, it's trying to find that OP balance that, according to the community SCH has been teetering on since day 1. And giving them some skills that just sound too OP from the start could cause issues. My suggestion is to look at all 3 and look to see what skills have correlations with one another. They dont have to be direct correlations, like the base heals, but sometimes more abstract things, like the lilies, cards, and the faerie.