yu-gi-oh cards egyptian god slifer deck Yugioh: Decks - Obelisk/Slifer 2 Set A single individual card from the Yu Yu-Gi-Oh! Egyptian God Deck: Slifer

I think Modern needs affinity to be better

Also there are many more cards like Force of Will and Gurmag Angler and the like in the constructed formats which further empowers Thoughtsieze

That being said, I think the reasons for a card being banned can be broken down into two main categories: A card is too powerful on its own and almost every deck has to have it to be good

Well, it looks like a Magic: The Gathering content creator is to blame

You have to get lucky to make the best of Harmonic Prodigy because, not counting prowess, there are only five wizards/shamans with relevant abilities you can copy with this card: one that provides treasures, two that give card draw, and two that give us temporary copies of our tokens