There are 4 main reasons why I think armagio is unbalanced and underpowered:
1- its very overpriced
2- it does not block weapons
3- if you have a shield, it is not protected by it (unlike Heal, which gives health that is protected by shields)
4- it can be bypassed with poison, momentum and spell damage (again, unlike heal)
I am not saying that the latter 3 should be changed, as this would make it almost exactly like heal. What I am saying is that because of these disadvantages, it should be stronger.
Edit: removed the first sentance because of what Ginyu told me.