It’s not an easy battle, but it’s mercifully short, although merciful for whom is debatable.
The Ice Demons showed Jack no mercy, they’re shown little in return, but at least they don’t have time to suffer the way Jack did. Ianto supposes that’s a kind of mercy.
Flamethrowers are brutal but efficient, lasers slice cleanly, fire grenades…
They only use one; they have more but they’re simply not needed. The Ice Demons misjudged humanity; thought them easy targets.
They found out too late they were wrong.
Victory brings Ianto no joy, just the grim satisfaction of a job well done.
TBC in ‘Cleanup’