One hero takes out all 5 with one hit

[Sorsha]

They discuss Colens and Azlars firestorm skill in this tread as well.

Firestorm = "I Win" Button

So firestorm is pretty much an “I Win” button. If I’m raiding someone and that goes off, my entire team is dead within 3 moves or less. Anywhere from 50-75% or more of my team health is gone instantly and the rest burns off quickly. There are other way overpowered abilities in this game, but this is by far at the top of that sordid list. If any devs read this and/or care, please consider reducing that attack’s effective ability considerably.

Some also think that it is too easy to win when it’s fired.
Maybe this helps.