Chinese fighter jet engines are supposedly already better than the best Russian jet engines they've been given, though. General perception is that the WS-10 is generally better than the AL-31FN, hence why they started replacing AL-31s with WS-10s, both in domestic and export aircraft. The WS-15, if it does get even close to it's design goals, would be significantly better than any Russian engine.
They seem to be struggling a lot with airliner engines, yes, but they've only recently even considered making them. Even then, the WS-20 has entered service, and if it matches claimed specifications, it's as good as anything Russia has either.
The recent leaked picture showing a J-20 with dual WS-15 puts their development on par with F-119/F-135. Lets see how quickly they can ramp up production. It seems they have fixed their supply chain issues.
It seems easier to make an engine that gives very high power at the expense of efficiency than an extremely efficient engine with reasonable power which is what airliners want.
In the Pacific, efficiency is the main goal for fighter jet engines. The goal of the WS-15 is to have F-35 level efficiency while being able to go relatively far in the supersonic regime and outrange every US plane.
And of course the engines for strategic lift planes are based around efficiency first.
I could believe the J-20 could match the F-35, and apparently the Air Force could believe it too because there’s also the F-22. And strategic lift planes use normal jet engines not supersonic ones so they face the same issue as Chinese airliners do.
The F-22's engine are not as good as the F-35 engine. It gets around that by simply being a larger plane and having a second engine.
Both modern fighter jets and airliners use turbofan engines, the difference is the bypass ratio (hence the size of the bypass blades). For both low and high bypass, Chinese engines are supposedly better than Russian engines. They aren't better than Western engines but they're not that far apart. As far as airliners, the airliner engine is a different design from the WS-20 because of different requirements. It started development far later than the WS-20 and it has been flight tested after only 5 years, which isn't bad at all.
They seem to be struggling a lot with airliner engines, yes, but they've only recently even considered making them. Even then, the WS-20 has entered service, and if it matches claimed specifications, it's as good as anything Russia has either.