I am British and for the British its a god send, we have now the most capable carrier borne aircraft in the world capable of EW and AAW, its a bit crap as sea-strike and grand-attack. However in the future any nation with a carrier without the F-35 will be at a huge disadvantage.
In terms of the air force, it doesn't matter much. Because air forces are mostly defensive and stealth has a limited use in air defence. I would much rather Britain put is money into an air defence network with ships, mobile launchers and radars and static radars/launchers. This is the main weakness Britain has, no air defences at all.
For Turkey you are in a difficult strategic environment. You have Russia/Ukraine/ Syria/Greece/Israel around you. I would have have stayed in the F-35 program. The problem is the US congress is only interested in milking the F-35 for their donors to get rich, so they make changes all the time to push costs up. There is no doubt at this point like the F-22 the F-35 is the best jet in the world. Now you have drone swarms, you have the S-400 and S-500 of the Russians which will be able to shot them down. However no other aircraft is close them.
I just dont see a scenario where Turkey would enjoy its advantages. I get that it is the most technologically advanced out there but for what good?
Sometimes having your weapon so advanced is a disadvantage for the maintenance and take off cost and the risk that you take by possessing it.
I dont think anyone is willing to see whether their stealth is useful against S-400s neither.
In terms of power projecting, yes they are useful at that but it is not an urgency for Turkey at the moment.
I may have swallowed some government propaganda for saying this but indeed it seems like keeping the air contested enough and going for the drone swarms with cheap but plenty systems sound like the ideal strategy.
The only bad I see is our fellow Greek neighbours having the advantage in Aegean but again, they wont be able to take off those F-35s as much as we do due to money.
For the proxy wars vs terrorist groups, having to take off F-16 for each convoy was already a pain for the price and the pilot. F-35 would be a setback on that problem as well.
Also the biggest problem was the potential kill switch and having to be accessed by the Americans to use the plane. Turkey is a country that was and is under American embargo.