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Guzma had no real redemption. We get a glimpse and hint at where his story might go but no real closure.
Like Guzma, Plumeria was a type specialist but was a rejected trial captain. Cool, that's a good way to establish both characters. Plum, though, goes beyond that. Guzma is presented as kind of a fuck up and easily duped. He is suckered into Lusamine's plot which makes him seem like an even bigger fool. Plumeria cares about Team Skull and the grunts. She calls them her little brothers and sisters. When she is beaten before the final stretch of the game she continues on to better herself as a trainer. She appears as a challenger for your championship title too. It's evident she has come a long way from the battle on Route 15. She has new additions to her team and, more importantly, her Golbat evolved. It shows that her bond with the pokemon was strong enough to evolve it. She even says, "Even when I give it my all, I'm nothing compared to you! Maybe my Pokémon and I need to go through more together to deepen our friendship. I'm out of here, Champ." It shows she is still trying and willing to be a better trainer.
I dunno, I think Plum was the better character overall. I wish we got to see more of Guzma.