I wanted to make a general post about the challenges of designing compelling and balanced healer abilities. But it became clear there were far too many elements to discuss. We can save those for another post. Instead I'll talk about one that has been a challenge for me when trying to design anything that isn't a "continuous" ability, and in general anything that breaks from the current healing formula to perform something really meaningful.
Many people lament that abilities don't take enough advantage of sespus, but the problem is without some kind of cooldown system (which is another topic altogether) anything that uses spirit ends up being improved by respia as well as sespus. You end up with the same "problems" as our current system, regardless of how effective you make the ability. Note I haven't done the math for any of this so I'm at "well informed player" levels; take it with a grain of salt.
As a result of this, most suggestions I hear (or come up with) that try to encourage sespus have at the very least a side effect of being a big buff to high respia healers. And in addition any idea that attempts to increase heal speed without including faustus training raises huge red flags, but that is probably a topic for another post.
Just to summarize my opinions on healer abilities that I was going to write at length about. I generally agree that new abilities need to encourage trainers other than what the typical healers train, or at the very least not devalue them. That includes sespus. They should also open up new specialties and options for healers either tactically (on the battlefield) or in a training strategy sense.
It is just a real challenge. One that most other games also face. I think the real solution will end up being branching away from strict "healing" as the only ability of every healer (which is how most other games approach it). But that has to be done very carefully. And it still doesn't change the respia/sespus debate.