The "big six" of FDX, UPS, SWA, DAL, UAL and AAL will be the very last to feel any pinch in pilot supply, well after you begin seeing it in on-demand cargo carriers, DHL/Amazon contract carriers, ACMI airlines, regional airlines, and ULCCs.
Why? Because these six airlines provide the best compensation, benefits and career progression and will draw from every source of qualified pilots available.
I wouldn't hold my breath for the "pilot shortage" to factor at FDX anymore than I would for single pilot Part 25 operations to provide relief from such "shortage".