Maverick brings early disruption (Daze, Force of Will, Fatal Push, Cabal Therapy) and efficient threats like Orcish Bowmasters that punish our cantrips, so we want to lower our curve of clunky value pieces. Thoughtseize helps us proactively strip their interaction or a key Hogaak/Dark Matter Manipulator threat before we go off. Boseiju, Who Endures answers Urza's Saga or problematic noncreature permanents and doubles as a land, so it's a free upgrade over a clunkier artifact. Song of Creation is risky against their Wasteland-heavy, disruptive manabase since it forces discard at end of turn when we may not have gone off yet, so it comes out along with excess Giant's Boulders that are too slow against their proactive clock.