Someone way back hit it on the head when they said most flow through agreements are biased to the mainline. With the exception of the language Mesaba has (and good luck defending THAT if DAL furloughs), in most cases, more flow down than up. In most cases, flow throughs just provide a relief valve for junior mainline pilots.

When I was an MEC rep at ASA (~2004), the idea of a flow through/flow back with us was floated by the DAL MEC. We were unanimously against it for the above reasons, and I'm sure the ASA MEC continues to be.

Preferential hiring... good. Flow through... bad.