I am not sure about that. It depends on your withdrawal method on Upwork, and the amount. They do have a fixed wire transfer fee on Upwork of $30 (for people living outside of the US) which I loved because it's not percentage based. So if I tranfer a $5k from Upwork to my bank, it would be less than 1% which is perfect.
The only option I do on Fiverr is transfer it to payoneer, they dont take commission here. But when I transfer it from Payoneer to my swiss usd bank account, they take a fair commission.
For $2819, they took a fee of $57, which is approximately 2%, additional to the fiverr commission so that's around 22%.
That's all pre-tax of course.
But you get used to it.