These force your opponent to discard a card from their hand, and while this might not appear all that powerful at first glance, repeatedly forcing your opponent to discard cards or being able to choose a specific card from your opponent's makes discard effects worthwhile
The thing that places them so high on the list though, is that you can then pay seven mana, one of which has to White, Blue, Black, Red, and Green, to exile the top three cards of your library, and you can then play them without paying their mana costs
You can then swing out for a few turns with only your Waves to push past your opponents board
Its not 1 to 1 with your purchased cards, but on the bright side, you dont have to buy a real-life pack and a virtual pack