Actually the rates don't even seem that high (GP would make 80% of that right?) The total hours they've listed as completed would take me at least 13 years to complete, probably longer.
My actual lifetime average commission paid to Upwork is under 10% actually. People who repeat the claim about 20 (or 30! in this thread itself!) commission just don't read the rules.
I interpret the rules as "commission is 5% plus $550 per client", which makes it sound a lot lower. How much does it cost to get 1 client "from the internet"? I know the answer and it's not pretty at all.
And yes i'm on the platform for precisely 13 years, but bulk of money comes from fixed price contracts anyway, and effective rates there are ca. $300 an hour. Most of money was made in the last 2 years anyway.