Leather is preferable to synthetic, due to its better resisance to mechanical, chemical and thermal agression. So in case of a crashlanding or an on board fire, I would prefer a leather jacket. New is not Always better!
At the time world war 1 and world war 2 Leather was a popular material used across a wide breath of industry and wear.Motorcyclists usually prefer leather suits as if offers good protection and warmth. I think it was for those reasons fighter pilots initially wore them.
No, the Ejection seat did not change the risk of Fire the aim is still to try and get out of the jet before the Fire. But Fire risk is still present. Modern Aviation Flight suits issued by the Military are made of Nomex a material that is designed for Fire resistance. Fire risk and Aviation has not changed and will not. Additionally Most helicopters and fighter Aircraft are not pressurized or operated with open exposure.In the Case of Rotary wing aviation remember with the exception of a few token Russian types Almost none of the Worlds Helicopter use Ejection.But I think the main thing that made leather unnecessary was the invention of the ejection seat.
With those, pilots no longer needed to physically climb out of their cockpits to escape a dying (and often buring) bird. So their suits no longer needed to be able to protect them against fire.
With air conditioning, good insulation became less of an issue.
They were for many militaries phased out but have also been retained by many. Its a matter of choice and function. from time to time there have been synthetic jackets used in there place like the MA-1Leather flight jackets were most likely phased out in the west for cost reasons since they were no longer strickly necessary.
NO. The US military issues to it's rotary wing flight crews special uniforms sets. They are made in the Same Camouflage patterns for the Sake of Escape and Evasion.Those Apache pilots were wearing plain regular multicam, no different from army grunts or marine jarheads.
The USAF issues Leather Flight Jackets to it's pilots as does the USN and USMC. and others. out of Tradition and Function.That's less a sign of modernity and more of practicality. Go ask any western aviator and I doubt many would look down their noses at a nice leather jacket as part of their uniform than some here have.
I do remember that China doesn't have equivalant of Nomex fabrics, because if they do they'd have their naval crews issued with anti-flash gear, as well as protective gloves for fast-roping, and one-piece aviation suit, along with other things.