I always flew in airlines with airplanes manned by 3 crewmembers.
A captain, a first officer, and a flight engineer.
To a captain in these days, the most important other crewmember was the flight engineer.
After PanAm went bankrupt 1991, I had a one year contract as captain with Cargolux.
I was flying their older 747-271Cs... with a flight engineer.
Some of them got trained to become "cruise first officer" on the 747-400s...
But for that they had to get a CPL/IR...
They offered me to go to the 747-400 as a first officer for a year, then become captain.
I refused, I prefer the old 747 with 3 crewmembers, I still fly them today.
Most PFE - Professional Flight Engineers, few had a "pilot's license".
They had instead an A&P Mechanic certificate and maintenance experience.
Some flew privately, for fun...
Here in Argentina, I will not fly other airplanes. I have 5 years before retirement.
If they retire the old 747-200s, I will retire as well, my decision.
Airlines who fly 2 men airplanes in long range operations need 3 pilots anyway.
Two captains + a first officer, for flights over 8 hours duration.
The total salary of these three pilots is higher than 2 pilots + F/E...
Airlines DID NOT GAIN anything by supressing the F/E position.