Ibrahiim thank you for the input here, and the interesting notes on the explanations regarding the Irish/Scottish misnomer, which indeed often became somewhat misleading. Interestingly the events you mention with the Scottish mercenaries in Sweden and Norway reveal an interesting potential for the source of the basket hilts which became known as 'Highland'. It is further interesting that those sabres with basket hilts in Northern Europe became known as 'Sinclair' sabres in a further misomer having to do with one of the officers of Scottish forces in these campaigns.
In looking further into this sword of Cathey's, which is indeed an intriguing anomaly, I think the possibility suggested for the engraving having been done c.1790's is of course quite possible. I also feel that the sword was most certainly that of an officer in one of the Scottish regiments, as these men were given considerable latitude in matters of kit and weapons. In those times of course, supplying troops was the personal choice and responsibility of the colonels of their own regiments, and officers purchased their rank and commission, so given those circumstances it is quite understandable such carte blanche would be afforded them.
Perhaps the use of this earlier style hilt of English dragoons and in a Scottish regiment of cavalry would better explain the retention of the earlier sword and better placement of 1790s in its use.
While the engraving of this clearly pro-Scottish commemorative on the blade would seem bold, it must be remembered that Scot's are vehemently patriotic and proud, and such fervor, especially on the sword of an officer, would in no way be considered subversive. Things were quite different politically by then, and celebration of heroes of such early times was certainly allowable. While nationality was of course always an ever present notion, they co existed in these units as 'British'.
There was also some degree of national tension between Scots and Irish, but in battle, units such as Inniskilings and Royal Scots Greys rode together with great respect for each other in battle, in my own perception.
With regard to my apparent 'gaff' on the predominance of the broadsword as distinctly Scottish, in further looking and still not finding the source, I am thinking the comment (obviously too adamant) may have been geared toward 'typical' earlier Scottish basket hilts. As noted in German records, the Scots preferred heavy broadsword blades, perhaps more for their notably distinct style of swordsmanship , and that these clansmen were basically 'infantry' rather than cavalry. The single edged blade in my opinion became popular in the 18th century for dragoons (though these troops fought on foot mostly) and later cavalry for mounted combat.
The use of broadsword (DE) blades on cavalry swords was of course certainly occasional, but typically in the exceptions noted. Naturally blades used often lent to availability in many cases, so that might account for variations. Rehilting of hilts such as those found at Culloden might have been ersatz examples using either captured or otherwise obtained blades from perhaps English sources. Cross traffic in blades of course knows no borders ( I have a 'mortuary' with Andrea Ferara blade).
I think the comment on the broadsword (DE) blades would have been better worded as Scottish warriors pre Culloden 'preferred' those blades, and the term 'axiom' left out