Stop making ridiculous claims. No weight figures of the J-20 are available but based on size and most importantly fuselage height and width the J-20 will be an extremely heavy aircraft especially when fully fueled and armed. The WS-10 is far too underpowered for the J-20.
As for the J-20 easily beating everything, that's a bold claim (which you are known for making). If you compare the J-20s rivals, F35 and pak-fa there are some enormous challenges. Let's assume that the J-20 has the smaller RCS, the problem is the two mentioned aircraft F-35 and pak-fa will themselves be difficult to detect; especially since aspect angles of both aircraft play a major role since air warfare is dynamic.
For instance, every aircraft has it's optimal RCS angles; likewise, every aircraft has its less then optimal angles such as the rear. This means an F-35 or pak-fa can come in from the J-20s rear without the J-20 knowing it because remember the J-20 does not have a rear facing radar, yet the pak-fa does, it also has two side radars, this means it has full 360 degree situational awareness.
Optical sensors also play a role, we know that both the F-35 and pak-fa have sensors that can detect IR signatures from 100s of km away.
Counter measures also play a role as does maneuvering and kinetic. Whenever a missile Is launched a radar warning receiver will usually alert the aircraft, that aircraft will take evasive actions, acceleration, speed, and maneuvering can often cause a missile to miss or simply lose it's kinetic energy or simply put, burn out before it reaches it's target.
I can go on and on and even go into further detail but my point is clear. hopefully you can understand that it's not a video game and involves many variables.