How is that tracking different for a full time person vs a person who works for flex? Basically full time employment makes the workforce more sticky, and whatever performance quality process you run with the workforce will retrain or remove people who don't perform.

With flex, it's likely the same quality process, only the workforce is larger and more likely to churn. So no matter what the performance of the quality process it has some non-zero time to detect and correct worker performance, so I don't see how one avoids a larger rate of delivery faults just from the workforce dynamics.