The possible scenario's of Rafale's Vs J 20'S in BVRAAM's Secnario's
The Meteor uses a seeker of the same family as the MICA and ASTER missiles and is a known and proven technology. Also no aircraft is gonna fly straight into a missile while hoping it can jam it successfully - we will gonna see F-pole engagements which the ramjet will create a no-escape zone way larger than the Chinese PL-12 and PL-15 capacities. As for Meteor vs PL-12, that's a no-brainer, the PL-12 is roughly lower to an AIM-120B. The PL-15, on the other hand, features an AESA seeker and a dual-pulse rocket motor, sufficient to scare the USAF into the LREW program.
And? It's still a slotted array or pre-PESA radar. Its ECCM advantage is that it has a two-way data-link that can keep it guided by the Rafael. We're uncertain, basically, as to what the exact capabilities of the PL-15 are. The comparable Russian system, the K-77M, has a stated 197 km aerodynamic range, but is roughly the same meters to the PL-15. The minimum expected aerodynamic range of the PL-15 would be 200 km, likewise, but the extended length could result in significantly increased ranges; the MICA missile, for instance, is extremely long range missile's, but sports a 33% longer range (km vs 60km implied aerodynamic range) because of only a 7 kg difference (PL-10E has a listed 105 kg weight, the MICA has a 112 kg weight) and a 5G max maneuverability difference (55G vs 50G).
A further factor is that the standard NEZ of an AAM is about 1/3rd the aerodynamic range. But since the PL-15 is a dual pulse rocket motor, it can fire off its rocket motor in stages and further extend its NEZ over a conventional AAM. At 200 km range with 50% aerodynamic range, you get 100 km. At 250 km range with 50% aerodynamic range, you get 125 km. At 300 km range with the standard 33% aerodynamic range, you get 100 km. The difference between standard AAMs, dual pulse AAMs, and ramjets is that with standard AAMs you get one shot, with dual pulse AAMs you get two shots, and ramjets can continuously vary their thrust as long as they're within ramjet speed.
The main defenses of the Rafale comes out, first, to the Rafale having a modern IRST, being IOC-ed in 2009, with stated maximum detection / tracking at 100 km. This means that the J-20 can't approach the Rafale at high subsonic and has to do an F-35-style low-speed approach. Second, the Rafale is the only Western aircraft known to be capable of 11G emergency agility, which reduces the effective range of the PL-15.
When it comes to J-20 vs Rafale, the pure offensive competition is very close; the PL-15 likely matche's the Meteor in pure aerodynamic range, likely has almost similar effective range vs 9G based purely on its greater range, but is going to suffer a large range reduction vs a 11G fighter. Defensively, given that the Meteor isn't going to get an AESA seeker until 2022 at the earliest, and that the J-20 is at least a -30 dBsm VLO fighter, that the AESA on the J-20 is jamming capable, the Rafale is going to have a capability to easily detech the J-20.
Late to say, but still.