Not necessarily true ... the J-20 is underpowered relative to the F-22 but not severely underpowered. The F-119 has a thrust of 155 kN. Meanwhile, the most recent WS-10 variant thrust is roughly the same as that of the 117S, meaning over 142 kN of thrust. Since the weights of the aircraft are roughly comparable, the J-20 is only off by a mere 26 kN of thrust (13x2). A 180 kN WS-15 would then give the J-20 significant aerodynamic performance over the F-22 ... having said this, I think it would be pretty overkill tbh. A F-119 thrust class engine is more than powerful enough for a twin engine heavy air air superiority fighter like the F-22 or J-20. A 180 kN engine would be more targeted towards a single engine fighter than something like a J-20 IMO.