RE: 40k - Faction Pack - Space Marines - Detachment 3 - Firestorm Assault Force

You are not wrong!

In fact, the Adepta Sororitas have a Detachment called Bringers of Flame!

They get Assault on all their weapons and get +1 Strength when they are firing on a target within 6".

The Space Marines's Firestorm Assault gets that bonus within 12", so it is a bit better!