“The kings of England refused the colonies repeated requests to end slavery.”
Actually the Royal government issued two emancipation proclamations during the Revolutionary War.
Dunmore’s Proclamation of 1775 and the more expansive Philipsburg Proclamation of 1779.
Had Loyalists defeated the rebellion then slavery in North America would have ended 80 years before the Civil War.
While I amsure the British would have paid no attention to the rwo bits of wartime opportunism you cite, slavery would have ended here in the 1830’s if the American Revolution had failed. It is called the irony of history, Henry Kissinger is particularly fond of the phrase which means sort of a cosmic horselaugh at human asperations to control the course of events.