Spell Witch is a deck that stops every other control deck from being viable. We have aggro, we have combo, but the only reasonable control is Spell Witch. This is because Spell Witch will always dominate every other control deck. Spell Witch can beat you on turn 7-10, or it can prolong the game as long as it needs to get a good Dimension Shift > Rune Blade Summoner/Flame Destroyer. The longer the game goes on, the higher the chance you'll just lose next turn because of Dimension Shift. And Spell Witch has all the tools to make the game last as long as it needs. Regardless of if it's up against combo or aggro it can throw down 5/5 taunts, clear with Fire Chain, get through the early game with Glow/Magic Missile/Angelic Snipe/Wind Blast, kill a threat for free with Fiery Embrace, and draw whenever it wants for 0 with Fate's Hand.

In card games it's rock-paper-scissors: combo beats control which beats aggro which beats combo. Spell Witch is a control deck in nature, but is also technically a combo deck since Dimension Shift allows you to just have multiple turns at no cost. Most aggro generally just loses to Spell Witch unless the Witch got unlucky. Combo can beat Spell Witch, but only if they got their combo off before turn 7. No control deck will ever be better than Spell Witch because Dimension Shift doesn't have a minimum limit, or some other setback. The design space for control decks is, "Can this beat Spell Witch? No? Well, I guess it's not going to work then." Part of the reason why aggro is so rampant is because of this imbalance: the longer the game goes on the higher the chance Spell Witch has their win condition, which means control can never actually get to their win condition.