This does make Fractal decks more expensive and it does slow down fractal,mono, and duo decks (in order of magnitude)
However you have to remember, how many cards do you play in a turn? At the beginning of the game we have a full hand, 7-8 cards, hopefully half filled with pillars. Then we draw 1 card per turn (with the exception of time) with about 1/4s of the cards being pillars.
So with this setup only decks that are waiting for a one turn mono combo, or fractal deck, or mindgate decks would be playing more than 1-2 cards per turn after this is out.
If a fractal deck faces up against this they would cautiously play only 1-3 of the newly fractaled 8 creatures per turn. This slows down the deck but doesn't deny or shut them down completely. All in all a decent 1 card nerf.
Since this card is other and since it hurts mono and duo decks it would most likely end up in a rainbow deck. If an mindgate deck faces up against they would hesitate on playing more than 1-3 of a stolen creatures per turn, rather they would delay some of the stolen creatures till next turn. This barely would slow a mindgate deck down.
Over the course of a duel this card will create small penalties that would add up but probably not as quanta draining as a single devourer.
For a cost of 6|4 other (which translates to about 2|1.33 mono to compare to devour|pest 2
) this card is balanced.