To give you a very simple rundown... In XC3, each class has 5 skills, and you pick 3 of them to use in battle; you do not get all 5 at once. Once you master a class, 2 of those skills can then be equipped onto any other class in the game similar to the old cross class system, and you can equip up to 3 skills from other classes to use on the one you're currently using for a total of 6 actions in battle. Then you also have a Talent Art which is effectively a limit break that charges different based on which role your class is. Attackers charge off performing positionals, Defenders charge off using aggro generating actions, and Healers charge off placing field effects.
War Medic is the healing-focused healer. Its skills, simply put are the following:
Multi-Blast is an AoE attack that heals in an AoE around you if it hits.
Heal Bullet is just an AoE heal.
Advanced Cooldown is a field effect that increases defense while standing in it.
Cure Bullet is an AoE status removal.
Vital Bullet is an AoE delayed healing buff.
Technical Heal is their talent art and it's a bigger AoE heal basically.
War Medic's a good early-mid game healer, but it's outclassed by the mid-late game healers.
As for the concept, I don't recommend looking at that as a complete entity. As I said, I was really just trying to think of ways to adapt the tools apparent on the Tactician class and on Taion, not trying to create a completed idea. As for what has MP costs or what is instant cast, I just wanted to specify those when I felt it was important for the idea. If something doesn't list an MP cost or cast time, I don't really know if I'd make that free or instant cast at this time. It's fine to discuss what they should be, though. But I also mentioned that the kit is incomplete. If anything, it at least needs a Raise spell.
This is the kind of mentality I have going into a design. The thing is, I do not have access to a prototyping build. I cannot test these things. That is an essential step to actually shipping a new job or a job rework or anything of the like. That's why I don't try to get wrapped into the balance of those numbers that harshly. That's also how building a new job or a job rework actually goes as well. You often start by shooting for the moon and seeing how that looks, then reeling back in different aspects to maintain balance. I promise you there have been iterations of every job at some point that were incredibly broken that we've just never seen because that idea was brought into a testing build and ironed out. If something like potencies, cast times, or MP costs are odd, then that's absolutely something we can talk about, but the most important thing is the design--how something plays.