Perhaps some amount of repayment for education is reasonable, but not this amount.
How many American doctors are paying >75% of their AFTER TAX income to pay down those debts ?
None.
How many Cuban doctors agreed to the arrangement of being restricted to a country controlled by the Cuban government, and therefore only offered a pittance for their services ?
None. They were born there.
What would happen if a bank offered such a deal to a US citizen ?
They would be persecuted, as this falls under "usury" and is a crime. Note: it's a crime. As in, if a bank does this and gets convicted (which happens regularly) people WILL go to jail for doing this.
What would happen if I did the same, organising a job for you in a foreign country and in return I get 75% of your wages in a contract that couldn't be broken ?
You could go to a judge and get the contract annulled, as this clearly violates labor laws. The article seems to confirm that this indeed violates even Brazilian labor laws.