They're building their own engine as well: https://en.wikipedia.org/wiki/ACAE_CJ-1000A

I agree that the C919/929 pose no threat as is, but the Chinese are clearly playing the long game here and their massive domestic market coupled with government arm-twisting lets them scale: the C919 has already racked up over 1000 orders.

China is still at least 20 years behind on jet turbines. They can get the power or economy (in terms of use time/overhaul), but not both at the same time. Jet turbines are hard to reverse engineer, and you really just have to put the time in on materials engineering.

Probably the Chinese will have to rely on some derivative of the Russian PD-14 engine. It is very probable that the chinese will lose access to western engines due to sanctions in the not so remote future, and their indigenous projects are still very far behind the state of art in jet engines.