you are talking absolutes, that is the reason people sometimes do not understand each other, Gambit never said DSI intakes are less or more stealthy in absolute terms, both systems have stealth treatment, both have compromises, the Caret intake type requires more RAM, more maintenance, more money, it is harder to make, Lockheed chose the DSI to replace it on F-35 simple because is cheaper to maintain and make, not because is more stealthy, all shapes do reflect radar, flat plates or bumps will reflect radar, the advantages of flat plates is they send a strong signal only in one direction, a bump or sphere, send the signal in all directions, but it weakens the signal because it distributes it into many directions.
From a top view the F-22 shields the intake duct, the DSI does not do that as well.
In general terms, J-20 does not follow the rules for stealth treatment as F-22 does, but do not take it in absolutes, it was done intentional, it is not because the Chinese engineers do not know them, they do understand them but stealth does not go all the time well with aerodynamics, plus stealth imposes a weight penalty, that requiere more powerful engines, thus the Chinese engineers needed to balance aerodynamics, the engine thrust available with stealth, they sometimes gave priority to stealth, sometimes to aerodynamics and engine thrust, where you have less stealthy features is because aerodynamics and engine thrust were higher priority, its canards, ventral fins and the rear part of it are such parts