There is significant difference between Steely Resolve and Not of this World. Steely resolves forces you to spend 2nd turn playing your protection instead of searching for your combo pieces. On the contrary Not of this World is nice surprising trick to punish the opponent who kept just Karakas or single removal without FoW. It is also better topdeck in the turn when you need to go off. Yes, the card is not MB material. Not at all. But definitely deserves the SB slot as it does exactly what we need exactly when we need it. In my opinion this card is better than discard spell in the matchups where Not of this World actually matters,