Entirely different purposes
The J-10 is mainly for Air to Air combat
It's purpose is to intercept incoming flight arrivals into it's airspace
It's take off is among the fastest , yet it's range is only around 60?80 Kms radius from take off point and sustained air combat reduces effectiveness (It's single engine)
It's mainly as a first line to intercept enemy aircraft
Rafale is a Multirole fighter
It's purpose is offensive
It's used to hit surface or marine targets relying on speed and durability of its twin engine
Nobody will use a J10 to intercept a Rafale and and would prefer using Surface to Air Missiles and Anti Aircraft Defense Systems
J10 is primarily used against Mig 21 Bisons and F-16s
Rafale is primarily used against Surface Targets like Terrorist Camps or Army Groupings or Civilian or Military Infrastructure like a Bridge
It's biggest enemy would be the S-400 system or the HQ-9 Read Also : What's an animal that looks adorable, but is extremely dangerous to humans?