Todd (Cajunscot) wrote: “I have no issue with the Irish wearing the kilt; the issue I have is with the myth of the kilt as ancient Irish dress.”

On this point you (and Matt) are entirely correct, of course. But I do feel that the philibeg is a natural development of the breacan feile, and so also of the Irish brat.
And while there is much argument around the English engineer Rawlinson (I think I read that Matt dismissed him as being entirely mythical), I am persuaded that on balance of probabilities he did work in mines in at least two Scottish counties, and had a tailor make up a philibeg.
After all, he was married to a Scotswoman, and wore Scottish dress. It seems highly likely to me that he, as an outsider, had an insight into how it could be simplified or rationalised.
Strapping on a philibeg is far simpler than the laborious process of belting up a breacan feile, even if the typical Highlander did have some means of maintaining the pleats.
I do not see the logic of dismissing his invention as a claim by the Sassenachs that pulls the rug of Scottish tradition (or inventiveness) out from under the Highlander’s feet.
Regards,
Mike