Everything is a compromise. If you can update smaller plane's FBW and aerodynamics, it will be preferable - see MiG-29K.Basic design has good AoA pointability and low speed handling characteristics. That's very essential for a carrier fighter and makes a lot of difference for carrier take offs and landings. Much better to take a large fighter with high AoA at low speeds over a medium fighter that does not perform as well on that envelope.
Or simply J15 is total rubbish and PLAN is not happy and looking for alternative
even the carrier trainer never materialised
There could be a under lying problem
The MiG-29 is a beast. The Su-33 was a tamer carrier aircraft.
The fact that F-14 outperformed in many ways F-4 and F-18 did not lead to switching the carrier wings exclusively to F-14. One of the reasons being also the sheer size of the F-14.A Flanker outperforms a Fulcrum in every metric, speed, climb, dive, turn, AoA, payload, radar performance. Its the pinnacle of the non stealth fighter jet generation. One should consider the Su-33 has even better low speed and high AoA performance than most Flankers, even the canard ones, at the expense of a higher top and cruising speed --- higher lift wings are more draggy for a trade off.
There was only one navalized platform that was available that China could reverse engineer i.e the SU-33.This. The flanker platform is a very very good one, one I’d say (assuming it’s upgraded) it is 2nd only to the J-20 and F-22. There’s a reason China chose it as it’s heavy fighter contract instead of developing another plane.
Of course what makes a fighter better is mostly performance of subsystems. I'd imagine the latest flankers from China and Russia totally dominate Eurocanards since many are close to a decade old now. Sensor fusion is the buzzword everyone bangs on about without having worked on them or really understanding how it is developed for a fighter.
I'd wager Chinese and Russian sensor fusion onboard their latest fighters (J-20, Su-57, Su-35, J-16) easily exceed Rafale and Typhoon which came into service a decade ago. It's all software!
The fact that F-14 outperformed in many ways F-4 and F-18 did not lead to switching the carrier wings exclusively to F-14. One of the reasons being also the sheer size of the F-14.