Inferno vs Arrow Bomb

It doesn't. Only platforms surrounding the impact point will be affected, which is only a little bit bigger than its aoe range.

Edit: The fire field effect actually sounds nice, maybe mobs inside it would take summon-like damage, somewhere around 300base attack at max?

It used to do that. It was changed before it even got to GMS because of how overpowered it was. Now it's weaker than Arrow Rain, which makes no sense. Archers are supposed to specialize in distance attacks. Then again, just about every elemental skill in the game is horribly nerfed, probably because someone decided 1.5x damage was too much.