In fact, if you play vs a deck that has several copies of a card, this will increase your chance to get it from a spin. For example, AI4 decks are random, so its harder to get a card from a spin. Playing vs AI3, which uses constructed decks, increases your chances. This is because, if a deck has several copies of, for example, Dim Shield, spins can use more than 1 copy of it, and so getting 3 in the wheels has a higher chance.