Dominaria has an important non-saga mechanic, of course: historic, its replacement for Kamigawa’s focus on legends. The cards in Dominaria that are necessary rather than exceptional by themselves are enablers for historic (mostly low-mana cost common artifacts). Basically, these fill the gaps when one basicallyto draft around legends, but there wouldn’t be enough legends to really be able to make that happen, so you throw some artifacts in and the deck works better. It’s basically a limited-only distinction between “legend matters” and “historic matters,” and I can’t remember any time that the “historic” designation has come up in my recent games of Standard. (Maybe that’s because mono-red, the deck I play against half the time, doesn’t build around anything other than making a life total equal zero.) I respect that historic was necessary for Dominaria to work in its emphasis of legends, but I think Rosewater exaggerates its importance ; a lot of those cards that seem like the backbone of the mechanic aren’t even played often in draft. Players aren’t tripping over themselves to draft enough Powerstone Shard to make their decks function in the way that Lorwyn drafters consistently moved their ratings of Changelings (the gold standard of a limited backbone mechanic) higher and higher.