I do think it’s disingenuous to compare the Emancipation Proclamation from an abolitionist (and Lincoln was, no matter the spin confederates try to put on it) to a ploy by a British governor

I’d probably conflate Dunmore’s Proc with the First and Second Confiscation Acts. They both served as tools to undermine rebellious states without upsetting slavers still in their purview. The Emancipation Proclamation, and then the 13th Amendment, were expansions of the policy made afterwards by Congressmen who recognized there couldn’t practically be a thin sliver of slave-legal states in between the abolition states and the confederate ones.

It certainly didn’t free all slaves in the Empire

The UK abolished slavery in 1803, following a domestic wave of abolitionism that spilled over into the Northern US states. The abolitionist movement didn’t end at any one border. Activists recognized abolition as a global struggle, one big reason why the UK failed to align with the Confederate States despite doing a lucrative textile trade on the backs of American plantation captives.

And of course its worth noting how post-abolition colonialism largely exported the brutal practices of slavery outside the view of UK/US consumers. That doesn’t change how public disdain for slavery as a practice influenced governors like Dunmore, Kings like George III, and eventually Presidents like Lincoln to employ abolition as a weapon against political enemies.

This wasn’t one thing or another. The moral revulsion generated by slavery made slave liberation and instigated slave revolts a popular tool of foreign powers and local dissidents. The politics of abolition were never exclusively a strategic or exclusively moral decision.