You seem to believe that China's military ambitions are purely defensive, but that is not the case. They have grandiose expansionist ambitions which include basically the entire South China Sea - which in spite of its name is shared by many countries. Not to mention their explicit goal of eventually conquering Taiwan. Their military doctrine is fundamentally offensive and does require air power.
In other words, let's says the Chinese military jet engine is 15 years behind is say fuel economy. Which reduces range. If the conflict is local that doesn't matter overmuch.
Equally operating from land, not carriers, reduces reach, but if what you want to reach is local then that doesn't matter.
If China has military ambitions (and despite the sabre rattling there's no overt indication of that), they are all in a specific area.
By contrast the US likes to participate in, or instigate, actions far from home. Moving planes means long open-ocean ferry flights. Single-engine reliability, range, effeciency and so on is paramout.
Equally the US relies on friendly local countries to provide support bases, logistics, fuel and so on. As evidenced just this year, that support can be withdrawn. Will Japan or Korea want to be dragged into a US / China conflict over Taiwan?
So if the Chinese are operating engines later than the first gulf War, and on par with the second, I'm not sure that's a defining difference.
The US doctrine of air-defence suppression followed by air superiority may not be possible in a space near the Chinese mainland.
Supercruise also matters a bit less when the distance to combat is shorter. Less fuel expended on "getting there" is more fuel for "on station". Plus, assuming more-or-less unlimited supply of machines and pilots means more flight hours on station.
So while the engines play a part in a hypothetical conflict, supply lines (and the length thereof) play (I think) a larger part.
Maintenance hours are sure to matter in a real war where equipment is getting destroyed and supply lines are being disrupted.
The difference isn’t huge (I think it’s 10-20% or something), but when fuel is your main cost that’s enough to make older engines undesirable
China may or may not be much more than a decade behind in their engine technology, but there's no commercial case for designing a new aircraft with engine variants so outdated they wipe >$100m off the sticker price of the aircraft....
A 10-20% reduction in fuel burn is actually considered pretty huge...
(This applies a bit less to military engines though, where performance is a more important factor. Fuel efficiency is still important though)
Also, the domestic commercial jet market is still sizable, so excluding the domestic market from analyses is kinda weird.
Finally, lots of countries are spooked by arbitrary US sanctions and want to diversify.
With petrol/diesel engines they just gave up and went straight to electric, but there's no viable alternative to jet engines for planes, so they'll put in the work (plus the military incentive running in parallel)
No, but regional aviation can be well served by electrification - a jet engine needs to run at a speed it pushed enough air through itself to propel the plane forward, but a turbine feeding a generator that powers a couple electric motors can run at a far more forgiving regime.
As pointed out elsewhere, all it might take is a paradigm shift to unseat the current incumbents.
This isn't really true. Chinese ICE vehicles are also sold worldwide, and Geely has some genuine ICE engineering achievements:
https://www.autoblog.com/news/geely-just-built-one-of-the-mo...
The only use case is modern day AI workloads, but that's used more in planning than in the field. I can imagine a use case for e.g. image recognition, but again, that tech or the level required is not new at all and doesn't need state of the art chip tech.
That's also why they're so damned expensive, and why it's difficult for upstarts to break into the market with cheaper alternatives. Like any tech company, once they get the customer locked into a platform they're constantly pushing upgrades to both stay technologically competitive and, more importantly, keep their margins high.
That’s one of the reasons drones are so disruptive. The development cycle is tuned by state of the art missile and stuff, and isn’t tooled for some dude strapping a mortar round to a little drone.
in which conflicts have those air defenses proven themselves?
But unless you massively subsidize a company "cough Rolls Royce cough" then you can't compete at all with a generation or two behind commercial jet engine tech.
Do they need to be at the same level as the West?
For civilian aircraft a decade or two behind seems like it would be good enough.
For military aircraft that could be a significant disadvantage, but from what the net is telling me they have excellent air defenses so it seems unlikely someone with superior planes is going to be able to go in and bomb them into submission. And they have a lot of nuclear missiles to further discourage anyone from trying.