If you are familiar with the longer-term trends in the British Empire re slavery at that time, in 1772 slavery had been prohibited within Britain and the abolitionist movement in the empire as a whole was gaining steam. They had a variety of self-interested reasons by the 1770's or so to seriously question slavery. On the one hand in the Carribbean English smugglers were growing rich illegally trading massive numbers of slaves out of the British empire into for example St. Domingue (at the time a major colony of the French and their biggest direct competitor in the region), which was having the adverse effect of fueling Britain's competitors. On the other hand, there were increasing concerns being voiced in Britain about the limiting effect of unwaged workers on market demand. Additionally they had massive military concerns about preventing large slave populations from rebelling in case of a foreign invasion or general social instability, as was not unheard of (less than a decade after the conclusion of the American revolutionary war the slaves of St. Domingue rose up and overthrew French rule in that colony, for example). Purely on self-interested grounds the political climate in Britain was beginning to militate against slavery. None of this is really above 100-level college history course material.

I really doubt the British would have been much kinder to the native peoples in the long run, either.

There is literally no reason to believe that the British would have been any kinder, considering that Canada was built up as a British colony (technically still is but at this point exercises complete self-government) and is not really any better. I'm not pro-British. In 1763 the British concluded the French and Indian War, and as part of negotiating peace with those indigenous nations that had taken up arms against them agreed to freeze further settlement of the western frontier for a time. This was just a cost-benefit calculation for the British because the war had been costly, they had incurred a large war debt that needed to be paid off, and they also had a larger empire to consider. Many of the American colonies were plantation economies and would continue to produce wealth that could help pay down this debt, so the British empire had no immediate pressing need to expand the colonies. Peace with indigenous nations was preferable in the short to medium term so they could regroup for further assaults in the long term. This kind of maneuvering was common throughout the history the British empire.

I only bring this up to point to the contradictions between British capital and British-American settler masses that aspired to petit-bourgeois status. The settler masses just wanted land now and en masse ignored the treaties their government had signed and would illegally cross the frontier and squat on Indigenous land and attack indigenous people of their own accord. This was a constant political problem for the British, since this threatened their negotiated peaces with these nations, leading them to attempt to intensify policing along the frontier, leading settler masses to feel frustrated and "oppressed" by the British.