Comparing the MiG-31 with Rafale is like comparing Bruce Lee with a Para Special Forces commando.
Sure Bruce Lee was much faster with his arms & legs but he couldn’t operate 14 different kinds of guns, run 40 km with a 25 kg backpack, navigate through jungles, perform special recon behind enemy lines, kill anyone just with a kitchen knife & rescue hostages.
The MIG 31 is absolutely a good platform, no question, However it’s just a Interceptor, While most of the Pakistani and Chinese Fighters can be countered very easily by the Sukohi’s and ground based missile systems, the Pakistani F 16 Block 52 armed with AIM 120 AMRAAM can easily chase the MiG 31 and it down, the same goes for China with Su 30 MK with R 77 missiles can easily kills the MiG 31, unlike Russia, They need to engage large number of NATO planes and High flying Reconnaissance drones, with the long range Air to Air missiles, and High altitude of flight, The MiG 35 can easily shoot down almost all kind of recon drones and other recon platforms like AEWCS and U 2 Spy plane.
The Interesting matter is because of the R 33 Long range radar guided missile, The MiG 31 can able to destroy any long range US made Bombers, While US has comes with large number of Bomber fleet, The Russians found a Long range Radar guided missile to counter them, The High power Zalson Phased Array Radar in the MiG 31 can easily tracks and guide missiles over 300 kilometers, they demonstrated the capabilities by destroying a cruise missile using the R 33 Zalson combo, the same can be used for destroying enemy satellites too,
The aircraft would comfortably fly above mach 2.5 (top speed mach 2.83) with a sole mission to intercept western strategic bombers like B-52. Hence it is designated as an interceptor aircraft.
On the other hand,The Dassault Rafale is a French Twin-Engine,Canard Delta wing,Mulitrole fighter aircraft designed and built by Dassault Aviation for wide range of short and long-range missions, including ground and sea attacks, reconnaissance, high-accuracy strikes and nuclear strike deterrence.
Indian Rafale will be a modified version of the F3R standard that is currently on track towards qualification and validation in 2018 by the French government and military.
The F3R Rafale is centered around integration of the MBDA Meteor beyond visual range air-to-air missile, the Thales TALIOS laser designator pod and the laser homing version of Sagem’s AASM Hammer air-to-surface munition. The F3R also includes attendant software upgrades to on-board sensors and avionics.
The Rafale can only fly at Mach 1.8, but speed is not something that defines the Rafale. What defines the Rafale is its ability establish aerial supremacy, perform reconnaissance missions, ground attacks, suppress enemy air defences, anti ship strikes & even initiate nuclear deterrence. Hence it is called Multirole Combat Aircraft.