For me, number one takeaway is, "he has a worker paid 600/700 usd per month (superstar)" who I suppose is generating much more value than 7% (700 of 10000).
So the copywriter has shouldered no risk either. He's also free to try and get more per word but he might be in a place where 0.05USD/word is actually pretty decent income.
I mean, imagine you work for a company and come up with a change that saves a million a year. Surely you don't expect to receive that million, do you? On the other hand, it's not your problem if sales go down this quarter, since your contract pays fixed salary.
of course it is, you can get laid off.
Capitalism works by siphoning off value that workers generate and putting it into the pockets of their employers. You're right that employees are (somewhat) insulated from risk in this scheme, but I don't think it's crazy to suggest that someone is entitled to more than 7% of the value they generate.
Sure, not my problem. Everyone's problem.