The relative scarcity of these different treatments is not considered part of the card's rarity
Sphere Grid, on the other hand, is fantastic in counters-matter decks
Based on this experimenation, it seems like the Sapphire/Steel deck is more aggressive , with new cards boosting Strength and increasing Resistance, while the Amber/Amethyst deck is more about mitigating and removing damage
Interestingly, the Void is also included within the Final Fantasy universe, but is not represented as a crystal like these other elements
There's so much looting and rummaging that you get to churn through your deck quickly, reducing variance and making sure you find the cards you need (and discarding the ones you don't) reliably, WITH ONE MAJOR EXCEPTION (see The Bad) It's very consistent
Scions & Spellcraft (White-Blue-Black) Be a master caster and gain control with card advantage as you band together with Yshtola, Nights Blessed to aid Eorzea in its time of need