Are you sure? We know the R-73 can intercept AAMs, it would certainly be an interesting insurance, in case some enemy manages to put a missile in range to hit the MiG.
MiG-31s are not expected to meet enemy fighters.... the PVO had both MiG-31s and Su-27s so I would suspect any risk of air to air combat the Su-27s would be vectored in to the fight rather than the 31s.
I would say they r heavy fighter-inteceptors- they defeated Libyan Su-22s & MiG-23:
Hahahaha... those heroic F-14s shot down two Su-22s when one of the Su-22s dropped a drop tank and the brave heroic F-14s panicked and thought they were under attack. In reality there was zero chance of an Su-22 starting combat with an F-14 by launching an AAM at them head on...