I can't speak for Adeline because I only got her to orange and stopped equipping.
As for Volt, his attack steal skill is ~1000 attack power at level 100 which won't wear off until the end of the battle. For HoL that's very nice to weaken the attacks of the enemy step by step. His ultimate scales with the stolen attack power as well. On the other hand, his defense isn't the best - but he's standing behind most of the other frontline heroes.
After he get's awakened he starts to shine with his "whole enemy team energy drain". That's the reason he's often used as a suicide tank to steal the whole enemy team over the half of their energy (numbers need to be confirmed though).
"Comments reflect the opinion of their authors and in particular are not suitable to justify a legal decision."
Level 100, 98k rating, 642 stars
Guild leader of
Server 11-24, 87 wins - 7 loss