Thoughtseize proactively strips their key disruption (Daze, Force of Will) or other important cards like Kaito, Bane of Nightmares before they can deploy their plan. It can still be countered by Daze or Force of Will, so try to cast it with spare mana up. It does not answer Hogaak, Arisen Necropolis, since Hogaak can be cast from the graveyard and a discarded copy is still a threat. Orcish Bowmasters punishes their cantrip-heavy draws (Brainstorm, Ponder), which trigger it on each draw outside their first draw step, and its enter-the-battlefield ping can kill small creatures like Stitcher's Supplier. Once Upon a Time is weaker here since we need interaction more than card selection against their proactive disruptive shell. Quirion Ranger is a minor value engine we can trim for more impactful disruption.