Well, who says "upgrading" a card makes it more efficient based on its original element? Upgrading just makes cards different. It's true we've seen that a lot of cards get cheaper to cast or activate, but that needn't always be the case. Pulverizer is a good example of this too: It's no cheaper in Earth quanta to cast, but it's cheaper in Gravity quanta to activate. Is that good for Earth players? Not necessarily, but it is good for Rainbow players. And, by the same logic, if you're running a few Electrum Hourglasses, it might actually net you more cards to be spending some Light quanta to activate your Sundials...
