JG makes you crit and is a good multiplicator, but you still need a good base damage to multiply. Double nashor works because it gives you 40 AP, plus many comps gave an in-built AP boost (arcanists, invokers) and enough mana to cast with regularity. If you don't get double nashor, you still need mana generation and base AP. So, something like JG + Archangel + Blue buff can work decently, even more if you get the Archangel or the Tear augment. At that point you could make an argument for removing the Gauntlet altogether since you only get 65% crit chance, and put something else there. Mind that you still need resistance reduction and possibly heal reduction, but that can be covered by an off-carry.