Thanks for a great insight, I'd never seen that before.
What I have seen is that George Washington himself expressed concern that British offering freedom to slaves for service would win Brits the war, and that was Washington's justification for matching them.
I've also seen where Washington's army at Yorktown was reported as 1/4 African Americans, but, iirc, those troops had recently moved from New York to Virginia and so we must suppose they had been recruited mostly from Northern freed-blacks.
But your insight that British use of fugitive slaves lost them loyalty amongst Southerners is new to me, will have to mull that over a bit...
I'm not so sure about that. You'd have to check it state by state and region by region.
I assumed the loyalists lost out because of a mixture of British atrocities and better patriot commanders. My understanding was that loyalists mattered more in North Carolina, where slaves were less of a factor than in South Carolina, where they mattered more, but I'm no expert on any of this.
Maybe it was more of a passive thing: if you were a large slaveowner with Tory sentiments, you probably wouldn't commit yourself openly to the loyalist cause if you knew it would mean losing your slaves.
But, strange though it may seem now, more loyalists came from the middle and lower rungs of the social ladder than the higher ones. A lot of them were Scots who'd already fought the British and lost and weren't inclined to go through all that again.
Anyway, so far as I know it's not been proven, but it's well worth examining more closely.