I’m sorry, but this, in my eyes, is a ludicrous statement.
How was the British Empire anything but extremely exploitative? I’m sure when you ask either Indians, or Chinese, Africans, they well tell you something quite different. Let alone the Native Americans or Native Australians.
The moment an Empire needs an entire island at the other end of the world just to store its criminals, I would call it extremely repressive - and that’s only its own country, not even its colonies!
Let’s face it: The vast majority of what we today accept as official history is what has been written by all the British Lords, officers, colonial landlords, etc, painting the picture of the harmonious lord/servant. Of course they wouldn’t see anything wrong with the Empire.
Your statement seems to be largely based on the fact that there has been no other Empire that managed to expand as far as those of the Britons and keep it for the period of time the Redcoats did.
You can hardly compare the situation in a country that has been occupied for maybe a couple of years with one that has been occupied for several generations!
Also, regarding positive impact:
I don’t see that - especially not the most. You could argue that even the Romans outdid the Britons in this regard, bringing advanced mathematics and architecture, such as Aqueducts to the conquered nations. What good, by comparison, did India learn from its British conquerors, other than the rules for Cricket?
Even today, take a stroll through Buckingham Palace - anybody should get sickened by the continued proud display of the cultural and historical treasures stolen from dozens - if not hundreds - of peoples over the centuries and denied from their rightful owners. This is, of course, not only a British occurrence but can be found in almost all European and American museums.
This is not meant as a complete riff on the British Empire - but rather a (slightly overreacting) counterargument to your little claim.