Some Commonwealth countries in Africa continued to allow chattel slavery until the turn of the 20th Century. And British Hong Kong had its own peculiar form of indentured servitude (called mui tsai) that wasn't banned until the 1920s that allowed the buying of young Chinese girls to be kept as household slaves/servants until they were emancipated through marriage .
So Huzzah! for 'Ol Blighty!
For another example of British hypocrisy don't forget about their shipping many tons of opium into Chinese cities and destroying the social and economic fabric of that nation. The Chinese wrote to Queen Victoria begging her to stop the shipments of opium into China, but these letters were intercepted and she didn't see them.
Opium was making them too much money. Much of the wealth of the Victorian era came from Chinese drug addicts selling everything they could to pay for their addictions.
China was the "sick man of Asia" for a reason, and that reason was British men wrecking them with drugs.
Appeals to morality don't work. Threats to money streams elicit instant reactions as the Opium wars illustrate.
They do deserve credit for it, it's just that we have to keep in mind that it was after all six decades after the separation of Independence. And the rest of what you stated.
We Americans were abolitionist before they were. - This fact right here would be a huge problem for progressives if we weaponized it. They've geared their false historical narratives in the exact opposite direction and in such a way that they cannot reverse it. It's a one-way road for them and it is such a weakness. Such a weakness.
I regard this as low-hanging fruit, ripe for the picking.