While I fundamentally disagree with your title, how epic would it have been to see a cutscene of the Order of Praxic warlocks gathering thousands of guardians to retake the moon? Even if Crota basically slaughters everyone. Or even an intro cutscene to introduce Eris arriving at the tower. According to the grimoire, Zavod, the Speaker, and others, are extremely concerned with her dark obsession with the hive. Bungie really missed an opportunity to have some sort of confrontation at her arrival. Even dialogue alone would have fleshed these characters out, and given them context other than stationary vendors.