Plenty of decks rely on a single big threat, whether its Troll of Khazad-dm or Tolarian Terror
Ultimately, the goal behind this change is to make opening packs more exciting, with even more beautiful cards to hunt for and a greater opportunity to find the special Epic quality cards, as they are less rare than the current Enchanted type
There's enough incidental life gain and legendary creatures in the set for her to work reasonably well, but she's not going to be super powerful since life gain is more of a sub-theme than anything and her stats are bad
But the first copy of either is usually no detriment to your deck the Map in particular is so mana efficient that Id always prefer it to adding extra basics in my splash color
You can activate the mana ability of a Treasure even if you have nothing to spend that mana on
You draw just one card, no matter how many creatures are attacking you and your planeswalkers beyond the second