I don't think any system would be able to do this very well. For instance, some players let spells go off so that they can either spellsteal the benefit or consume it for resources (i.e. DH). Alternatively consider the case of using spell reflection on a damaging spell to turn casted spell back on the mob.
IMO instead of trying to make/find systems to evaluate player ability, the better path is to keep track of good players during your PuG runs and become friends with them so that you'll always have a pool of "good" players that you can find them to do runs with.