While forcing players to pay an extra mana to put burden counters on it may not sound like a big deal, for decks like Rakdos Midrange that would normally slam the card turn four, the extra mana can be a big deal
I could certainly imagine the card simply being banned just because it doesnt make for enjoyable play experiences, and having seen Aetherworks Marvel loom over Standard once before, its not hard to imagine it being too good as Turn 4 Emrakul, the Promised Ends and Ulamog, the Ceaseless Hungers are soul-crushing and game-ending
Crucially, the art in this tier is the existing art found on regular cards, simply expanded to eliminate the border
Sharuum the Hegemon + Sculpting Steel/Mirrorworks + Glassdust Hulk/Arcbound Crusher = infinite damage Ashnod's Altar + Sword of the Meek + Thopter Foundry or Krark-Clan Ironworks = X: get X 1/1 fliers and gain X life
Its also worth remembering that core sets tend to be defined by a couple of high end reprint anchors-the sort of gee-wiz inclusions that are designed to entice established players into buying a box of a set that they might otherwise skip
Splinter Twin is probably the one with the most traction re: Twitter buzz, but it was banned because it invalidated a lot of linear strategies