Thoughtseize lets us strip a Daze or Force of Will before going off, which matters enormously against four copies of each. Song of Creation is too slow against a deck full of cheap interaction, and its two-cards-per-spell draw hands Orcish Bowmasters plenty of triggers. Keep Giant's Boulder in. Keep Veil of Summer in since it stops their Daze and Force of Will from countering our spells and keeps their black Fatal Push from targeting our permanents on our key turn.