Which means that they have reserves sitting around collecting reserve guarantee while lineholders soak up most of the open time. Every pilot who drops flying creates at least an opportunity for a reserve pilot to use up some of his guarantee, thus saving the company that much money.

One guy, maybe. But I don't see how it would be the case that a significant number of pilots in a poorly manned category could do so. Their only likely option would be QPDs or the Swap Board, and to the extent that the ALV is likely to be high in such a category, many pilots would have little room on their schedule under the FARs.