The Armenian parts sound interesting, but:
Also, ü is seen in Nuristani and as a stage in Dardic (such as ü > we or ö > yo from umlaut). This presence in IA suggests that rúçant- = bright/shining S; could be caused by ü (perhaps reg. if only short u>ü and üK(>Y)V with analogy in most words).
…this bit seems anachronistic. u > ü in Nuristani and Dardic is probably a fairly recent areal feature, since it has parallels also in modern Iranian, e.g. u > i in Southern Pashto (but not other dialects) and ū > ʉ in Tajik (but not Dari, Farsi or Middle Persian).
_j.