Without going into too much depth because this is mainly about how you are presenting your theory: I think your case could be stated more simply and perhaps with less potential for confusion.
This type of Omani sword has dated examples from as early as the ___ century. (I'm not sure what the earliest example with provenance is, perhaps the grave find you mentioned). Stylistically it likely takes influence from Abbasid designs, which were introduced into the region in the mid 8th century. The form closely resembles these early period swords and seems to have changed little from them. It has a tradition as a heraldic symbol within the Omani Ibaathi tradition which may account for the longevity of the form in Omani culture. Most extant examples likely date from the 17th to early 19th centuries.
I think in the absence of hard evidence, e.g. archaeology, dated examples etc. it's important to leave things just a little open ended. After all, it's impossible to be sure, although you've constructed a sound theory to explain this particular form.
Just intended as constructive comments and I hope you'll take them that way.