Dimir Midrange is full of counterspells like Counterspell, Force of Negation, and Spell Snare, plus efficient disruption from Thoughtseize and Fatal Push, so this is a grindy matchup where you want resilient threats rather than more removal. Warping Wail can exile an Orcish Bowmasters or Psychic Frog early (both qualify via power or toughness 1 or less at some point, Orcish Bowmasters is 1/1) or counter a Preordain. Grafdigger's Cage is a minor hedge against any graveyard shenanigans, but is a lower-impact include here. Sire of Seven Deaths and World Breaker come out since they are clunky top-end cards that are vulnerable to counterspells, and you would rather have cheaper, more efficient action against their disruption-heavy shell.