Duress proactively strips their removal (Requiting Hex and Stir Up Trouble) along with other key noncreature cards like The Misty Mountains Cold, Obsessive Pursuit, and Lively Dirge before they can disrupt our plan. We Say Thee Nay! is too slow against their steady curve of efficient, cheap creatures, so we swap it for more proactive disruption. Azure Beastbinder stays in, since its evasion and ability to shrink a big blocker or attacker are still useful here.