Izzet Delver wants to grow Dragon's Rage Channeler and Murktide Regent into fast clocks backed by free counterspells, so we prioritize efficient removal over value plays. Erode kills Dragon's Rage Channeler or Murktide Regent outright at instant speed, which is exactly the kind of answer this matchup rewards. Flickerwisp is cut since a 3/1 for three is too slow against a deck trying to race us with efficient burn and evasive fliers, and it dies to a single Lightning Bolt.