I understand why you don’t like Slytherins really....
Rowlin made a quite good job to depict them -almos all of them...-as unbearable, arrogant and unfaithful people. (despite I think Piton’s one of the best chara in there, and in some way one of the most loyal ones... He stay loyal to his love ‘till death literally, showing a sort of ‘Hufflepuff’ attitude).
But you know... I like to see the light in the dark and the good potential in bad assumpionts, and I see in Rafael the best ‘in goods’ application of Slytherin’s qualities. Ambition without too much arrogance. Sassyness without contempt. Cunning and calculation without bad faith. And a really big, well hidden and shelter, heart.
Let me make a little joke here, to show you how I see the ‘slytheriness’ in Barba, compared to other charachter’s attitudes.
Olivia and Amanda (the Gryffindor ones, 100%. Both): “Rafa! We HAVE to condamn this vile bastard! He’s totally guilty, we know that! We looked him in the eyes! We don’t give a fuck about evidences, we’ll have to punish him no matter what!”.
Carisi (the Hufflepuff one, 170%): “Tell me what I should do to frame this coward, and help you, and save the victim, and the whole world in the meantime, and I’ll do it!”
Barba (the Slytherin): “Guys... i feel you. I really do! This worm should go in jail, and the victim needs justice but... I can’t win. So I’m sorry but I won’t pick up the case.”
This is just a joke, like I said.
It’s really schematic and simplistic. And not always true.
In fact, sometimes Barba picked up a case he wasn’t sure to win because he felt it was the right thing to do.
Like you said, no one fits 100% in just one House description, and everyone could be a mix of 2 or more.
But still, I can’t help myself to see in Rafa the best Slytherin I’ve ever met.
(He and Dworkin too. I love them both so much.)
PS I’m really happy you’re french because italian and french haves a quite similar sentence structure. Probably you understand my ‘english’ much more than english people.