The funny part is that I can't find anything disagreeing with my point in your post, so I guess, this will walk right into the "misunderstanding"-box. What we can hopefully agree on are certain examples: Tolkienverse magic would not allow for fireball throwing wizard duking it out while they levitate above the ground. It would not allow someone to conjure up a magic-shield and use it to block catapult fire. Neither would it allow regular people to... I don't know, to literally turn yourself into a dragon or some of the ancient monsters of the deep? That's basically what I mean with "hard-control".
The way I thought about it resulted in putting a fire-resisting armor in exactly this category, since that is pretty much what I understand of a magical shield. To be fair though, since Edain already has this rune magic (see below) such resistance could work. Aulë's point is therefore also a valid approach as far as I can tell.
Still: The doors just turn invisible when not shine upon by the moon! Since that is a pretty special situation (see below) and also not that far away from what real matter can do (fluorescence, anyone?) if for the mystical touch, I'd say that these runes' actions are pretty subtle. Meanwhile, stopping direct damage directed towards the carrier of certain armor is a pretty direct and "in your face"-method. ;) Two points to support this further:
1. We are talking about dragonfire! That stuff is literally able to destroy rings of power! My point is, rune-magic (if it even exists this way!) needs to be insanely powerful to not utterly useless, otherwise the dwarves would probably forget about it in the first place. Which brings me to number 2...
2. I'm sorry, but there is ZERO mentioning of this sort of direct protection by runes! And if they were able to accomplish something as powerful as protection against dragonfire, dwarves wouldn't just ignore this. This way runes could very well stand on the same level as mithril and that already reads "plotholelium 1337" in our modern language. xD
To conclude: I know, I haven't answered all questions or to the entire reply, but I'll note the following: All examples you gave in your post, I'd put in the "subtle" or in the "powerful entity" category. Also, I'd like to make clear, that making something mildly effective against fire is definitely possible.
"See below"-part:
The thing about runes is, I understood them a little different: First apart from 2 (?) gates at Moria and Erebor we don't know much about them, therefore the margin of statistical error in our interpretation is quite large, so to speak. Secondly, both these locations are very special locations being the two really great dwarven kingdoms, so that alone was for me reason enough to not question their power -there are numerous examples in the LotR or Tolkien's work in general where a situation is the deciding factor about what a spell can do; both Moria and the Erebor should be special enough.
TL:DR: Yes, the dwarves (and other races too, for that matter) could probably craft an armor that is moderately effective against fire. And I'd say, that your idea how this could be accomplished, sounds reasonable, Aulë, eventhough I wouldn't interpret runes this way. Granted this point: The hunters of the Ered Mithrin are exclusively experiencing fiery attacks when up against firedrakes. This is the point where the knowledge of craftsmanship starts to break down, including rune magic.