The Aura version too often didn't have a target or the available target wasn't a good choice for the Aura
Spells like Transpose capture the abilities of specific jobs (in this case, the black mage's transpose ability) and uses the mechanic rebound to cast it again (the ability's cooldown)
Once Prismari is out, each one also becomes much more threatening because the next spell is going to copy itself for every spell that came before it
Omniscience - makes every card in hand free post-trigger
Deep Gnome Terramancer is a low-cost flash creature that will slot right into Death and Taxes builds, helping you keep up with other decks as they ramp
I counted all the differences: take the 38,768 unique cards, account for 58,779 in additional foils and treatments, plus 718,172 non-English cards, 5,278 non-playables (the tokens, art cards, etc.), 755 playtest cards, Arena's 221,930 cards in their languages, and 29,252 MTGO cards and you arrive at our total of 1,072,934