The ceiling is not quite as for Arc Trail high but is none the less surprisingly close and more importantly it is much much easier and more common to reach or get near that ceiling and early in the game too
On top of that, Emrakul never had to exist in a format with powerful graveyard hate along the lines of Rest in Peace, Leyline of the Void, or Scavenging Ooze, and the presence of those cards gives opposing decks much more ability to fight back against Emrakul
Each card has its own unique abilities and strengths, and when you play them at just the right time, you can turn the tide of the battle in your favour
Sometimes youll cast it just for indestructibility to save your creature(s) or something, but that isnt nearly as powerful most of the time
Its certainly a card that Im keeping my eye on right now, but I just dont see it