Hi David, great explanation and thank you.
I acknowledge and accept your main points above.  My only argument is that the term "British Isles" is being used as a substitute for a more accurate term.  If we substituted the word "Europe", we would lose the point that this was the first anglican bishop to not swear allegiance to the British monarch on behalf of a "province" outside the kindoms controlled by the British monarch (in enemy territory).  The scottish anglicans were still within the area (Kingdom of Great Britain).  As a note, the relevance is those two points taken together - not swearing allegiance *and* not being in an area controlled by the monarch.
BTW, what is the connection between the consecration of Samuel Seabury and the founding of the new province?  Is it assumed that the new province was recognized immediately?  If so, what is the relevance of representative clergy from nine dioceses meeting in Philadelphia to ratify the church's initial constitution in 1789?  Is this the actual official founding of the province?
If you are happy to substitute the term with kingdoms of Great Britain and Ireland as a compromise, I am fine with that.