Each bracket has a set of deck-building conditions: if a deck meets those conditions, it sits in that bracket
The primary function of both cards is to cheaply draw lots of new spells for use in decks that will use all their resources quickly
That seems pretty insignificant in the face of potentially being able to overcome a disadvantage of going in first in battle, though
Vodalian Illusionist (Mirage/Visions/Weatherlight) Part of the charm of bounce is that your opponent will have to reinvest resources to recast that creature a following turn
Both are also good later on, especially the Twisted Abomination, whose regeneration is great in giving you confidence to swing at a busy board
If you do, search your library for an enchantment card, put that card onto the battlefield, then shuffle