How long do you think he will last? He's never really proved himself as a world champion. I think he'd struggle with Valero or Fana.
Arthur is a C+/B- level fighter depending on how tough one rates fighters. His chin is very shaky, his defense is leaky, and his skills are nothing worth noting at the world class level. He's a large 130 pounder, but apparently he's having trouble making weight and his chin/stamina might suffer even more because of that when he has to defend his title in the future. Valero vs Arthur would be a good fight that could go either way. I would probably favor Valero because I think Arthur would have a lot of trouble with Valero's early assault and his chin wouldn't be able to handle flush shots from him. But at the same time, Arthur would be capable of outboxing Valero and hurting him as well. With the SFW division weakening, this is a good, realistic matchup. Soto would destroy him. Same with Barrios and Juarez. From the FW division, I would strongly favor guys like Linares, Guerrero, Luevano, John, and Jaendang over him. I'm confident Gamboa would take him out in 1 round if they fought today and the top LW's don't need to be mentioned with Arthur, because they're 3-4 levels above him. Hopefully he will take on challenges as a champion instead of defending his title against domestic fighters. Compared to a lot of C+/B- level British fighters, Arthur has taken a lot of risks in his career and seems to want to fight the best.