Wasn't the conventional wisdom behind the J-20 using canards was *because* the PRC aerospace industry's understanding of advanced flight stability systems wasn't yet deep enough to enable a canard-less/ventral-less design?
Nope, this isn’t really about whether the Chinese aviation industry is advanced enough for certain configurations. J-20 got its aerodynamic design because it is the one that best fits its requirements, just as the J-35’s aerodynamic design is best suited for its own role. Comparing the level of advance-ness by eyeballing the two airframes and counting the wing surfaces just isn’t going to give you a true and useful result.
To elaborate a bit based on my own limited knowledge, the J-20 is required to have a rather exceedingly large range, good maneuverability especially in supersonic ranges, good LO characteristics. It’s intended for combat environments that have relatively few sensors (AKA above oceans and such) and is geared more toward hunting down high-value targets than anything else in particular. The end result is a large airframe to hold enough fuel & weapon bays, canard-delta configuration with relaxed stability to reduce drag especially during the supersonic phase (where the aerodynamic center will shift aft) and all-moving tails to reduce the wetted area, weight and to have a larger moving surface to control yaw, possibly for advantages at higher mach numbers. The ventral fins are there because the all-moving tails are rather small for the J-20’s size and to provide yaw stability especially when at an higher aoa, when the tail-planes risk being blocked by the fuselage and wings. So as I said it isn’t about them being limited in ability and “have to have so many aero surfaces”, it’s about this configuration performing best in what the jet’s supposed to do.