except in that scenario You literally can never end the damage roll, and thus never do damage.
Re-read the features. its quite hilarious
EDIT: I was actually talking about the Battle engineer + vorpal dagger deal so nvm.
Vorpal doesn't apply to light blades.
Vorpal Glaive with Gauntlets of destruction does 9 damage per [W].
Vorpal Glaive without gauntlets does 6.67 damage per [W]
Glaive with gauntlets does 6 damage per [W]
Standard glaive does 5 damage per [W]
[sblock=Math]
Vorpal d4 with brutal 1 does Sum(i=0..inf) 3/(3^i) damage -> Converges to 4.5
Vorpal d4 without brutal 1 does Sum(i=0..inf) 2.5/(4^i) damage -> converges to 3.33
d4 with brutal 1 does (2+4)/2 = 3
d4 does (1+4)/2 = 2.5
[/sblock]
For comparison,
a Vorpal Fullblade with Brutal 1 does 7.7 damage per [W]
a Vorpal Fullblade without brutal does 7.1 damage per [W]
a Fulllblade with Brutal 1 does 7 damage per [W]
a Fullblade does 6.5 damage per [W]
[sblock=Math]
Vorpal d12 with brutal 1 does Sum(i=0..inf) 7/(11^i) damage -> Converges to 7.7
Vorpal d4 without brutal 1 does Sum(i=0..inf) 6.5/(12^i) damage -> converges to 7.1
d12 with brutal 1 does (2+12)/2 = 7
d12 does (1+12)/2 = 6.5
[/sblock]