The American Revolution wasn't against the King of England, it was against the traitorous Parliament who was using an incapacitated King as their prop.
Colonists were denied representation and were taxed by Parliament, not by the King of England.
George III wasn’t incapacitated during the AWoI. He didn’t have the first attack of porphyria until the late 1780s, some years after the AWoI.
But, other than that, yes, it was Parliament’s doing, not the King’s...
It was according to those who signed the Declaration:
"The history of the present King of Great Britain is a history of repeated injuries and usurpations, all having in direct object the establishment of an absolute Tyranny over these States."
It then proceeds to a long list of "he has" statement accusing the King of oppression.
As far as the article's argument, I believe the author is entirely correct that the Revolution wasn't a "just war" by strict Augustinian criteria.
But then almost no war has met those criteria. Very few wars have an utterly evil aggressor and a completely innocent victim. Most are started with at least some contribution by both sides. But the "mix" between the sides is important.
Per the "oppression" suffered by the Americans, it was by any historical or worldwide standard extremely mild. I believe the Founders revolted more out of a concern for possible future oppression than because that they suffered under was itself intolerable.