I would imagine it has to be random, but can't deny the Assassin/Gunner rare souls I've bought with Trooper points have been mainly garbage. The one I found in a secret location?
Prisoner.
Hmmm...
So also garbage
Gringo-4930
MOFO
Currently grinding for:
Odin(s) - Freya - Scrooge (Slauki) Ed / Moar Yggs