Blood can only be donated every 8 weeks, plasma twice a week. After donating blood, you can’t donate plasma for 8 weeks.
The hypothetical “untrustworthy” plasma donors you’re talking about are earning about $640 in 8 weeks. I don’t see them switching to whole blood donation for $50 or $100 compensation. I’m not seeing how the risk to the blood supply is going to increase at all, let alone significantly enough to exceed the risk of critical shortages in the blood supply.