With current materials technology, turbofans have more or less reached maximum performance for weight, fuel and thermodynamic efficiency, in engines like F135 etc. I'm glad China is investing heavily in and copying (when it can) materials and turbofan technology, but I also hope they're researching alternatives. Hypersonic vehicles and latest ramjet missile tests have been successful in the past so maybe there will be better aero engines in the future. Hopefully China will not be lagging decades when they do come out. Turbofans like WS15 in a flagship conventional warfare fighter like J-20 are always a morale boost and source of pride, but these days i'm sure China capable of at least starting to develop some super weapons for asymmetric warfare which will work their way into becoming mainstream weapons. Assassin's mace, ASAT, mini drones, EMPs, photonics based radars, hypersonic missiles, lasers, microwaves, DEWs... list goes on. Those are probably more important than immediate success of WS15 and J-20s in huge numbers. Hitler once thought of nuclear weapons as not worthy of serious pursuit. At one point, propeller powered fighters were considered more effective than jet powered because early jet powered fighters had many drawbacks.Not just that. But remember the whole Su-35SK was bought to get Saturn 117S for the J-20 hypothesis.
Yes the J-20 is very underpowered compared to F119 powered F-22 but the WS-10B gives the J-20 full independence and security. That is overall great news for such a critical platform.