From my experiences in DCS:
The R-60M has worked at all aspects. But more effective from a rear aspect shot.
The R-60M has inferior range than both AIM-9P and M. So for more effectiveness I fire it when within 3 to 1 KM.
R-60M loves flares, but not as much as the AIM-9P does. So fire it from a position where the enemy won't notice the missile coming to him, to avoid enemy deploying countermeasures.
Some pilots rely too much on the weapons, and don't put enough effort on tactics.
I'm sure there will be a few elite pilots out there that can deploy an R-60 way more effectively than most others shooting an R-27 or AIM-120.
MiG-21 will be an effective weapon against modern fighters in my opinion. It all depends on how the pilot uses the aircraft, if the pilot can't think or imagine how it is possible, then these will be the same pilots my MiG-21 will prey upon.
Obviously with a MiG-21 there will be necessities to change the tactics, but I plan to hunt flankers, fulcrums and eagles with my MiG-21 and I'm already confident the hunt will be successful! :)