What are you cutting for it, you're already running 4 Lava Dart. Lightning Bolt deals more damage, Mutagenic Growth deals more damage, it's not better than Expressive Iteration, Manamorphose, or Light Up the Stage, what are you going to cut for it? Lands? Creatures? Mishra's Bauble can't be cut because of Delirium, it deals more damage than Lava Dart if you have more than one Prowess creature, and it cantrips.

There is literally nothing to cut for Gut Shot. You can't cut lands from a Modern deck that's already running 18 lands and doesn't have some kind of land-bypassing gimmick, and you surely aren't going to be cutting any creatures for it.