We don't need to assume that, because Armenians became known as Armenians (exonym, not their endonym), then the root of the word Armenia/Armenian must have also come from Proto-Armenian roots or even from more broadly IE ones. It might well be that the Armenians were simply named by some people after some land they had come from when they first had contacts with that people, and this foreign population passed the named Armenia on to other populations, just like it happened to the various names for Greece in European and Asian languages.
So what you're saying is that Armani/Arman (and maybe Armenia itself) are related to Aram/Armen from an older source, but not derived from Aram/Armen. Makes sense. It does seem that (h)ar words mean "shining"/"white" or are associated with the sun in quite a few Indo-European languages.