FDX defined benefit isn’t going anywhere unless FDX ALPA negotiates it away.
Can’t speak for FDX, but Amazon air volume at UPS has increased even as Prime Air nears their 40th in-service 767. Both FDX and UPS are adding airframes and hiring pilots to support volume growth.
Single-pilot cargo ops are DECADES away; looks great in theory on paper, will be completely unreliable in operation for a multitude of reasons.
Sky ain’t anywhere NEAR falling on overnight express delivery.
That said, no commute plus AA’s massive retirement wave make it hard to pass up IMO.