Aren't their engines terrible?
I'm not sure it's hugely relevent though. The F35 procurement was structurally unsound. The result is an aircraft that's a jack of all trades and a master of none..
...or nearly none. I understand it currently holds a marginal and very expensively won advantage at long range air-to-air. Or at least it will once all the kinks are ironed out.
F-35 does something like Mach 1.6 where the F-15 Eagle hit ~Mach 2.5 and F-14 Tomcat hit ~Mach 2.4.
That's not because we can't make a much faster jet, just other compromises are vastly more useful.
Start combat at lower speeds and it's going to take even longer to hit high Mach.
Which is not to say it's useless, just not as useful relative to other tradeoffs.
Su-57 is still in infancy stage and judging from Russian problems, there's high chance it won't be around soon.
And for the F-35, it's easy to think of it as a dogfighter, but it's really intended more for the ground attack role. It can defend itself, but it's not going to be performing CAP when the F-22 or F-15s are around.
1. lives are relatively cheap
2. there is an ejection seat
3. most flights will complete without a failure
You can fight a war even if every flight has a 1% chance of a random engine explosion. There were worse odds over Europe in World War II.
GE decided to make passenger jet engines in China. There should be no doubt that the reliability (likely a function of the factory) will find its way back into fighter jet engines.
Regarding performance, that ought to match the Russian engines that were cloned.
Passenger jet engines don't really map to fighter engines. It's like comparing an F1 race car with a Volvo semi.