Here’s the thing—I feel that generally, writers tend to lean too much into the Rosinante was such a good guy he was so much better than Doffy he couldn’t hurt anyone. When this is very much contrary to what we see. Yes, I do think he’s much better than Doffy, I mean Rosi didn’t take over a kingdom, kill without reason, etc etc, he’s not outright evil. BUT. He isn’t the wholesome “smol bean” that many writers make him into. And don’t get me wrong, I think that interpretation is valid for an AU where things didn’t happen quite the same way they did in canon, I think that it’s totally incompatible with canon. Rosi was a Marine and we know even the best marines with what we are told to believe are the “best intentions” (ie Koby, Smoker, Bell-mere, Rosinante) they’re still part of a fundamentally unjust and evil system. (This dichotomy is something I love to see explore in fanfiction because it’s so fascinating.)
Not only was Rosi a Marine, but he abused the children of the Donquixote Family. Now: I understand that this was his attempt to prevent them from joining. To save them. However— he could’ve thought of a different way to do it that didn’t involve causing physical harm to children. And like we see later when he burns the hospital’s that reject Law, Cora is more than willing to hurt or even kill, to protect one person he cares about. He’s very much portrayed as a character whose moral code can be summed up by “the ends justify the means.”
Cora saved Law because he had the D in his name, but also because Law reminded him so much of Doffy as a kid. Law got lucky with this. Because Cora never tried to help Baby 5, or Buffalo, or the other kids, not after beating them or throwing them out a window didn’t work. He was willing to let them suffer the fate of being a pirate because the mission to get Doffy in jail was worth far more than their lives.
If Law hadn’t reminded Cora so much of Doffy, I think he would’ve just kept on his mission, never saving that angry little kid from Flevance, but saving Dressrosa from Doffy. (Was Law’s life worth more than all the citizens of Dressrosa? Was it because Rosinante blamed himself for not stopping Doflamingo even earlier??)
So all of this rambling to say,
Donquixote Rosinante is kind, loving, and caring, but he’s also selfish and manipulative and occasionally cruel. He’s far more like Doflamingo in some cases than I’m sure he’d be comfortable with. But they are brothers. And despite his limited story time, we’re shown a Rosinante who is flawed, nuanced, not just “a cinnamon roll” or a tyrannical villain. He’s messy, complicated, and human. And I strive to write him as such.