People love the class branch idea and come up with these suggestions fairly frequently (though less so recently), but they seem to miss a key point - skills from a base class can't be separated out depending on the branch you choose. This is why SMN has physick, even though it's so weak it's useless. If you try to branch a healer from GLD, you have to keep in mind this healer will have things like enmity generating melee combos with no way to separate that out. You really might as well just make a new class/job entirely, it would be easier than trying to cancel all the tanking abilities.
Now with that out of the way, there's a problem with "armored healer" in general. All tanks share gear within their role, and all healers. SE isn't likely to make custom gear for every content for an armored healer. Even if you take the approach that maybe they should share gear with tanks or melee, that introduces its own problems, eg, they'd be more survivable than other healers while potentially having useless stats - or if you make them useful, you have to balance that as a dimension entirely separate from other healers.
Now what you could pragmatically do is have heavy armor be part of the new healer's AF. However, that's not much of an identity in itself. Maybe you could make Chemist armored, or have a necromaner-healer that's armored, but just "armored" doesn't tell us much. But if you're envisioning a holy type healer with the holy pally thing... well, it's doable, but it would be tricky to avoid a lot of overlap with WHM.
As is, you can get fairly close to this by glamoring plate armor onto WHM (just you've got a staff instead of a sword). So to separate your idea from this, I would suggest fleshing it out a bit more. For example, are you envisioning a melee healer? If so, that helps give it a bit more identity. But we still need to know more about what this healer would do.
tl;dr: "armored" healer is a visual style (not class/job design) that you can have right now. To create a class with that theme, a lot more work would need to be done.