You're very right that it did. Everything that Oral Roberts did along the entire timeline of his career was nothing more than exploiting people to send him money. And if there's one thing people without a lot of money have, it's religion. If there's one thing they want, it's money. It's not very hard to part them from their money, all you have to do is tell them Jesus will give them more, if you give Oral Roberts more. It's a con and fraud.
Oral Roberts' use of seed faith did deliberately take advantage of poor and disadvantaged believers. That is how a lot of people like Oral Roberts get all of their money, is by exploiting the poor and disadvantaged because they do not know any better. He is one of the worst kind of people.
When Oral Roberts was challenged directly with the birth of a sick child that he could not heal, his system was devastated. Whether he believed he was a healer or not, whether he really was or not, that death was the ultimate sign that he was not in control of life or death. The Seed-faith principle was ruined because he could not save someone of a family that truly had supported him. This is the reason that seed faith became exposed as fraudulant, and preyed upon those that could barely afford to support it.
Oral Roberts' use of seed-faith did not deliberately take advantage of poor and disadvantaged believers. Roberts calls upon all people, including the poor to his to receive God's salvation. Those who answer to him do so out of free will. His ministries thrive on donations, and donations from the poor are just as valuable as those from middle and upper classes.
I do not believe Oral Roberts' use of seed-faith deliberately took advantage of poor and disadvantaged believers directly but I believe a lot of Christian churches and preachers are guilty of this. Some churches put a specific precedence on tithing and sometimes I see where that money is mishandled and often not put back in a way that the community as a whole benefits.