I'm not that up on the details but a lot of the former British empire like the US, Canada, Australia etc. are doing quite well. I was in Hong Kong in the 1980s and it did much better then under UK government than the mainland. Not sure about places like India. Ireland wasn't that great.
It’s complicated, because while yes the British were bastards, unlike some of the powers they weren’t completely rapacious, and recognized that at least a modicum of self sufficiency and good governance was necessary for them to have something to steal long term.
The French, Spanish, or (big yikes) Belgian colonies have had significantly harder times.
Kind of a ‘what did the Roman’s ever do for us?’ situation.
I get the impression a lot of the success was just providing some sort of rule of law and military security and then letting markets do their thing along the lines of Adam Smith's invisible hand of the market. (Scot who did some study at Oxford and died in 1790).
The old British Empire was hardly a an exemplar of free market economics. There were many independent companies but there were also chartered monopolies and price controls. We take basic economics for granted today but back then many leaders literally didn't understand the basics of how it worked.
The greatest feat of the ruthless British empire was the great number of independency holidays around the world.